scalar: adjust documentation to the microsoft/git fork

Scalar in Microsoft's Git fork can do a little more than Scalar in
upstream Git: in Microsoft's Git, it supports the GVFS protocol so that
Scalar can clone from Azure DevOps.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

contrib/scalar/docs/getting-started.md

@@ -18,8 +18,9 @@ Creating a new Scalar clone
 ---------------------------------------------------
 
 The `clone` verb creates a local enlistment of a remote repository using the
-partial clone feature available e.g. on GitHub.
-
+partial clone feature available e.g. on GitHub, or using the
+[GVFS protocol](https://github.com/microsoft/VFSForGit/blob/HEAD/Protocol.md),
+such as Azure Repos.
 
 ```
 scalar clone [options] <url> [<dir>]
@@ -68,11 +69,26 @@ in `<path>`.
 These options allow a user to customize their initial enlistment.
 
 * `--full-clone`: If specified, do not initialize the sparse-checkout feature.
-  All files will be present in your `src` directory. This uses a Git partial
-  clone: blobs are downloaded on demand.
+  All files will be present in your `src` directory. This behaves very similar
+  to a Git partial clone in that blobs are downloaded on demand. However, it
+  will use the GVFS protocol to download all Git objects.
+
+* `--cache-server-url=<url>`: If specified, set the intended cache server to
+  the specified `<url>`. All object queries will use the GVFS protocol to this
+  `<url>` instead of the origin remote. If the remote supplies a list of
+  cache servers via the `<url>/gvfs/config` endpoint, then the `clone` command
+  will select a nearby cache server from that list.
 
 * `--branch=<ref>`: Specify the branch to checkout after clone.
 
+* `--local-cache-path=<path>`: Use this option to override the path for the
+  local Scalar cache. If not specified, then Scalar will select a default
+  path to share objects with your other enlistments. On Windows, this path
+  is a subdirectory of `<Volume>:\.scalarCache\`. On Mac, this path is a
+  subdirectory of `~/.scalarCache/`. The default cache path is recommended so
+  multiple enlistments of the same remote repository share objects on the
+  same device.
+
 ### Advanced Options
 
 The options below are not intended for use by a typical user. These are

contrib/scalar/docs/index.md

@@ -28,10 +28,14 @@ these features for that repo (except partial clone) and start running suggested
 maintenance in the background using
 [the `git maintenance` feature](https://git-scm.com/docs/git-maintenance).
 
-Repos cloned with the `scalar clone` command use partial clone to significantly
-reduce the amount of data required to get started using a repository. By
-delaying all blob downloads until they are required, Scalar allows you to work
-with very large repositories quickly.
+Repos cloned with the `scalar clone` command use partial clone or the
+[GVFS protocol](https://github.com/microsoft/VFSForGit/blob/HEAD/Protocol.md)
+to significantly reduce the amount of data required to get started
+using a repository. By delaying all blob downloads until they are required,
+Scalar allows you to work with very large repositories quickly. The GVFS
+protocol allows a network of _cache servers_ to serve objects with lower
+latency and higher throughput. The cache servers also reduce load on the
+central server.
 
 Documentation
 -------------
@@ -42,7 +46,7 @@ Documentation
 
 * [Troubleshooting](troubleshooting.md):
   Collect diagnostic information or update custom settings. Includes
-  `scalar diagnose`.
+  `scalar diagnose` and `scalar cache-server`.
 
 * [The Philosophy of Scalar](philosophy.md): Why does Scalar work the way
   it does, and how do we make decisions about its future?

contrib/scalar/docs/philosophy.md

@@ -13,22 +13,27 @@ Scalar only to configure those new settings. In particular, we ported
 features like background maintenance to Git to make Scalar simpler and
 make Git more powerful.
 
-Services such as GitHub support partial clone , a standard adopted by the Git
-project to download only part of the Git objects when cloning, and fetching
-further objects on demand. If your hosting service supports partial clone, then
-we absolutely recommend it as a way to greatly speed up your clone and fetch
-times and to reduce how much disk space your Git repository requires. Scalar
-will help with this!
+Scalar ships inside [a custom version of Git][microsoft-git], but we are
+working to make it available in other forks of Git. The only feature
+that is not intended to ever reach the standard Git client is Scalar's use
+of [the GVFS Protocol][gvfs-protocol], which is essentially an older
+version of [Git's partial clone feature](https://github.blog/2020-12-21-get-up-to-speed-with-partial-clone-and-shallow-clone/)
+that was available first in Azure Repos. Services such as GitHub support
+only partial clone instead of the GVFS protocol because that is the
+standard adopted by the Git project. If your hosting service supports
+partial clone, then we absolutely recommend it as a way to greatly speed
+up your clone and fetch times and to reduce how much disk space your Git
+repository requires. Scalar will help with this!
 
-Most of the value of Scalar can be found in the core Git client. However, most
-of the advanced features that really optimize Git's performance are off by
-default for compatibility reasons. To really take advantage of Git's latest and
-greatest features, you either need to study the [`git config`
-documentation](https://git-scm.com/docs/git-config) and regularly read [the Git
-release notes](https://github.com/git/git/tree/master/Documentation/RelNotes).
+If you don't use the GVFS Protocol, then most of the value of Scalar can
+be found in the core Git client. However, most of the advanced features
+that really optimize Git's performance are off by default for compatibility
+reasons. To really take advantage of Git's latest and greatest features,
+you either need to study the [`git config` documentation](https://git-scm.com/docs/git-config)
+and regularly read [the Git release notes](https://github.com/git/git/tree/master/Documentation/RelNotes).
 Even if you do all that work and customize your Git settings on your machines,
-you likely will want to share those settings with other team members. Or, you
-can just use Scalar!
+you likely will want to share those settings with other team members.
+Or, you can just use Scalar!
 
 Using `scalar register` on an existing Git repository will give you these
 benefits:

contrib/scalar/docs/troubleshooting.md

@@ -18,3 +18,23 @@ files for that repository. This includes:
 
 As the `diagnose` command completes, it provides the path of the resulting
 zip file. This zip can be attached to bug reports to make the analysis easier.
+
+Modifying Configuration Values
+------------------------------
+
+The Scalar-specific configuration is only available for repos using the
+GVFS protocol.
+
+### Cache Server URL
+
+When using an enlistment cloned with `scalar clone` and the GVFS protocol,
+you will have a value called the cache server URL. Cache servers are a feature
+of the GVFS protocol to provide low-latency access to the on-demand object
+requests. This modifies the `gvfs.cache-server` setting in your local Git config
+file.
+
+Run `scalar cache-server --get` to see the current cache server.
+
+Run `scalar cache-server --list` to see the available cache server URLs.
+
+Run `scalar cache-server --set=<url>` to set your cache server to `<url>`.