Simplify contributing guide (#118)

* Update contributing guide

* Update contributing-guide.md

* Update contributing-guide.md

* Update contributing-guide.md

* Add .NET Core contribution bar

Documentation/contributing-guide.md

@@ -1,34 +1,22 @@
 # Contributing Guide
 
-Primary focus of .NET Core 3.0 release is to achieve parity with WinForms for .NET Framework.
-Since we're currently still porting parts of WinForms codebase (incl. tests) to GitHub, we're not ready to handle non-trivial or larger contributions beyond parity fixes yet.
+The primary focus of .NET Core 3.0 release for Windows Forms is to achieve parity with .NET Framework. Priority will be given to changes that align with that goal.
+
+We need the most help with the following types of changes:
 
-We plan to accept these kind of contributions during 3.0 release:
-* Low-risk changes, which are easy to review (e.g. typos, comment changes, documentation improvements, etc.).
 * Test fixes, test improvements and new tests increasing code coverage.
-* Infrastructure fixes and improvements, which are aligned with achieving our goal to ship high quality .NET Core 3.0 release.
-* Bug fixes for differences between WinForms for .NET Core and .NET Framework.
+* Bug fixes that specifically target partity between .NET Core and .NET Framework.
 
-If you have a **larger change** falling into any of these categories, we recommend to **check with our team members** prior to creating a PR.
-We recommend to first create a [new issue](https://github.com/dotnet/winforms/issues), where you can describe your intent and help us understand the change you plan to contribute.
+Please [file an issue](https://github.com/dotnet/winforms/issues) for any larger change you would like to propose.
 
-**WARNING:** Expect that we may reject or postpone PRs which do not align with our primary focus (parity with WinForms for .NET Framework), 
-or which could introduce unnecessary risk (e.g. in code which is historically sensitive, or is not well covered by tests).
-Such PRs may be closed and reconsidered later after we ship .NET Core 3.0.
+This project follows the general [.NET Core Contribution Guidelines](https://github.com/dotnet/coreclr/blob/master/Documentation/project-docs/contributing.md). The contribution bar from the general contribution guidelines is copied below.
 
+## Contribution "Bar"
 
+Project maintainers will consider changes that improve the product or fix know bugs (please file issues to make bugs "known").
 
-## Developer Guide
+Maintainers will not merge changes that have narrowly-defined benefits due to compatibility risk or complexity added to the product. We may revert changes if they are found to be breaking.
 
-Before you start, please review [WinForms contributing doc](TODO) and **[.NET Core contributing doc](https://github.com/dotnet/corefx/blob/master/Documentation/project-docs/contributing.md)** for coding style and PR gotchas.
+Most .NET Core components are cross-platform and we appreciate contributions that either improve their feature set in a given environment or that add support for a new environment. We will typically not accept contributions that implement support for an OS-specific technolology on another operating system. For example, we do not intend to create an implementation of the Windows registry for Linux or an implementation of the macOS keychain for Windows. We also do not intend to accept contributions that provide cross-platform implementations for Windows Forms or WPF.
 
-* [git commands and workflow](https://github.com/dotnet/corefx/wiki/git-reference) - for newbies on GitHub
-* Pick issue: [up-for-grabs](https://github.com/dotnet/winforms/issues?q=is%3Aopen+is%3Aissue+label%3Aup-for-grabs) or [easy](https://github.com/dotnet/winforms/issues?utf8=%E2%9C%93&q=is%3Aopen+is%3Aissue+label%3Aeasy)
-* [Coding guidelines](https://github.com/dotnet/corefx/tree/master/Documentation#coding-guidelines)
-
-To work in this repository, begin by observing the following:
-1. [Fork](https://github.com/dotnet/corefx/wiki/Checking-out-the-code-repository#fork-the-repository) and [Clone](https://github.com/dotnet/corefx/wiki/Checking-out-the-code-repository#clone-the-repository) this WinForms repository
-2. [Machine Setup](https://github.com/dotnet/winforms/blob/master/Documentation/machine-setup.md) instructions
-3. [Building](https://github.com/dotnet/winforms/blob/master/Documentation/building.md) instructions to build from source
-4. [Debugging](https://github.com/dotnet/winforms/blob/master/Documentation/debugging.md) recommendations and techniques
-5. [Testing](https://github.com/dotnet/winforms/blob/master/Documentation/testing.md) instructions, guidance, and rules
+Contributions must also satisfy the other published guidelines defined in this document.