doc: add CONTRIBUTING.md

Change-Id: Iaa903a33475e2f6d85d2914904e9cb9cf0333965
Reviewed-on: https://go-review.googlesource.com/5217
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
1 file changed
tree: 10475d5518a96bf4ef940876b9fcc7d7e7dfc147
  1. .gitattributes
  2. CONTRIBUTING.md
  3. README
  4. git-codereview/