Add project goals to CONTRIBUTING.md.

PiperOrigin-RevId: 362386747

CONTRIBUTING.md

@@ -3,6 +3,26 @@
 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