Update contributing guidelines.

* Align CONTRIBUTING.md with the google/new-project template.
* Explain the support story for the CMake config.

PiperOrigin-RevId: 421311695

CONTRIBUTING.md

@@ -3,30 +3,10 @@
 We'd love to accept your patches and contributions to this project. There are
 just a few small guidelines you need to follow.
 
-## Project Goals
-
-In addition to the aims listed at the top of the [README](README.md) Snappy
-explicitly supports the following:
-
-1. C++11
-2. Clang (gcc and MSVC are best-effort).
-3. Low level optimizations (e.g. assembly or equivalent intrinsics) for:
-  1. [x86](https://en.wikipedia.org/wiki/X86)
-  2. [x86-64](https://en.wikipedia.org/wiki/X86-64)
-  3. ARMv7 (32-bit)
-  4. ARMv8 (AArch64)
-4. Supports only the Snappy compression scheme as described in
-  [format_description.txt](format_description.txt).
-5. CMake for building
-
-Changes adding features or dependencies outside of the core area of focus listed
-above might not be accepted. If in doubt post a message to the
-[Snappy discussion mailing list](https://groups.google.com/g/snappy-compression).
-
 ## Contributor License Agreement
 
 Contributions to this project must be accompanied by a Contributor License
-Agreement. You (or your employer) retain the copyright to your contribution,
+Agreement. You (or your employer) retain the copyright to your contribution;
 this simply gives us permission to use and redistribute your contributions as
 part of the project. Head over to <https://cla.developers.google.com/> to see
 your current agreements on file or to sign a new one.
@@ -35,12 +15,17 @@ You generally only need to submit a CLA once, so if you've already submitted one
 (even if it was for a different project), you probably don't need to do it
 again.
 
-## Code reviews
+## Code Reviews
 
 All submissions, including submissions by project members, require review. We
 use GitHub pull requests for this purpose. Consult
 [GitHub Help](https://help.github.com/articles/about-pull-requests/) for more
 information on using pull requests.
 
-Please make sure that all the automated checks (CLA, AppVeyor, Travis) pass for
+See [the README](README.md#contributing-to-the-snappy-project) for areas
-your pull requests. Pull requests whose checks fail may be ignored.
+where we are likely to accept external contributions.
+
+## Community Guidelines
+
+This project follows [Google's Open Source Community
+Guidelines](https://opensource.google/conduct/).

README.md

@@ -131,6 +131,32 @@ should provide a reasonably balanced starting point for benchmarking. (Note that
 baddata[1-3].snappy are not intended as benchmarks; they are used to verify
 correctness in the presence of corrupted data in the unit test.)
 
+Contributing to the Snappy Project
+==================================
+
+In addition to the aims listed at the top of the [README](README.md) Snappy
+explicitly supports the following:
+
+1. C++11
+2. Clang (gcc and MSVC are best-effort).
+3. Low level optimizations (e.g. assembly or equivalent intrinsics) for:
+  1. [x86](https://en.wikipedia.org/wiki/X86)
+  2. [x86-64](https://en.wikipedia.org/wiki/X86-64)
+  3. ARMv7 (32-bit)
+  4. ARMv8 (AArch64)
+4. Supports only the Snappy compression scheme as described in
+  [format_description.txt](format_description.txt).
+5. CMake for building
+
+Changes adding features or dependencies outside of the core area of focus listed
+above might not be accepted. If in doubt post a message to the
+[Snappy discussion mailing list](https://groups.google.com/g/snappy-compression).
+
+We are unlikely to accept contributions to the build configuration files, such
+as `CMakeLists.txt`. We are focused on maintaining a build configuration that
+allows us to test that the project works in a few supported configurations
+inside Google. We are not currently interested in supporting other requirements,
+such as different operating systems, compilers, or build systems.
 
 Contact
 =======