README.md: Add a Windows-specific preamble

Includes touch-ups by 마누엘, Philip Oakley and 孙卓识.

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

README.md

@@ -1,4 +1,76 @@
-[![Build status](https://github.com/git/git/workflows/CI/badge.svg)](https://github.com/git/git/actions?query=branch%3Amaster+event%3Apush)
+Git for Windows
+===============
+
+[![Open in Visual Studio Code](https://img.shields.io/static/v1?logo=visualstudiocode&label=&message=Open%20in%20Visual%20Studio%20Code&labelColor=2c2c32&color=007acc&logoColor=007acc)](https://open.vscode.dev/git-for-windows/git)
+[![Build status](https://github.com/git-for-windows/git/workflows/CI/badge.svg)](https://github.com/git-for-windows/git/actions?query=branch%3Amain+event%3Apush)
+[![Join the chat at https://gitter.im/git-for-windows/git](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/git-for-windows/git?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
+
+This is [Git for Windows](http://git-for-windows.github.io/), the Windows port
+of [Git](http://git-scm.com/).
+
+The Git for Windows project is run using a [governance
+model](http://git-for-windows.github.io/governance-model.html). If you
+encounter problems, you can report them as [GitHub
+issues](https://github.com/git-for-windows/git/issues), discuss them on Git
+for Windows' [Google Group](http://groups.google.com/group/git-for-windows),
+and [contribute bug
+fixes](https://github.com/git-for-windows/git/wiki/How-to-participate).
+
+To build Git for Windows, please either install [Git for Windows'
+SDK](https://gitforwindows.org/#download-sdk), start its `git-bash.exe`, `cd`
+to your Git worktree and run `make`, or open the Git worktree as a folder in
+Visual Studio.
+
+To verify that your build works, use one of the following methods:
+
+- If you want to test the built executables within Git for Windows' SDK,
+  prepend `<worktree>/bin-wrappers` to the `PATH`.
+- Alternatively, run `make install` in the Git worktree.
+- If you need to test this in a full installer, run `sdk build
+  git-and-installer`.
+- You can also "install" Git into an existing portable Git via `make install
+  DESTDIR=<dir>` where `<dir>` refers to the top-level directory of the
+  portable Git. In this instance, you will want to prepend that portable Git's
+  `/cmd` directory to the `PATH`, or test by running that portable Git's
+  `git-bash.exe` or `git-cmd.exe`.
+- If you built using a recent Visual Studio, you can use the menu item
+  `Build>Install git` (you will want to click on `Project>CMake Settings for
+  Git` first, then click on `Edit JSON` and then point `installRoot` to the
+  `mingw64` directory of an already-unpacked portable Git).
+
+  As in the previous  bullet point, you will then prepend `/cmd` to the `PATH`
+  or run using the portable Git's `git-bash.exe` or `git-cmd.exe`.
+- If you want to run the built executables in-place, but in a CMD instead of
+  inside a Bash, you can run a snippet like this in the `git-bash.exe` window
+  where Git was built (ensure that the `EOF` line has no leading spaces), and
+  then paste into the CMD window what was put in the clipboard:
+
+  ```sh
+  clip.exe <<EOF
+  set GIT_EXEC_PATH=$(cygpath -aw .)
+  set PATH=$(cygpath -awp ".:contrib/scalar:/mingw64/bin:/usr/bin:$PATH")
+  set GIT_TEMPLATE_DIR=$(cygpath -aw templates/blt)
+  set GITPERLLIB=$(cygpath -aw perl/build/lib)
+  EOF
+  ```
+- If you want to run the built executables in-place, but outside of Git for
+  Windows' SDK, and without an option to set/override any environment
+  variables (e.g. in Visual Studio's debugger), you can call the Git executable
+  by its absolute path and use the `--exec-path` option, like so:
+
+  ```cmd
+  C:\git-sdk-64\usr\src\git\git.exe --exec-path=C:\git-sdk-64\usr\src\git help
+  ```
+
+  Note: for this to work, you have to hard-link (or copy) the `.dll` files from
+  the `/mingw64/bin` directory to the Git worktree, or add the `/mingw64/bin`
+  directory to the `PATH` somehow or other.
+
+To make sure that you are testing the correct binary, call `./git.exe version`
+in the Git worktree, and then call `git version` in a directory/window where
+you want to test Git, and verify that they refer to the same version (you may
+even want to pass the command-line option `--build-options` to look at the
+exact commit from which the Git version was built).
 
 Git - fast, scalable, distributed revision control system
 =========================================================
@@ -29,7 +101,7 @@ CVS users may also want to read [Documentation/gitcvs-migration.txt][]
 (`man gitcvs-migration` or `git help cvs-migration` if git is
 installed).
 
-The user discussion and development of Git take place on the Git
+The user discussion and development of core Git take place on the Git
 mailing list -- everyone is welcome to post bug reports, feature
 requests, comments and patches to git@vger.kernel.org (read
 [Documentation/SubmittingPatches][] for instructions on patch submission
@@ -43,6 +115,7 @@ To subscribe to the list, send an email to <git+subscribe@vger.kernel.org>
 (see https://subspace.kernel.org/subscribing.html for details). The mailing
 list archives are available at <https://lore.kernel.org/git/>,
 <https://marc.info/?l=git> and other archival sites.
+The core git mailing list is plain text (no HTML!).
 
 Issues which are security relevant should be disclosed privately to
 the Git Security mailing list <git-security@googlegroups.com>.