git-codereview: document short names in mail command

While we're here, fix bug in git-codereview gofmt usage message.

Change-Id: I547b8ae6fab01db1bc6b44b0e706d8faadbb60a9
Reviewed-on: https://go-review.googlesource.com/2781
Reviewed-by: Andrew Gerrand <adg@golang.org>
2 files changed
tree: a6070a25cc3b3541c08520bb855813565e0b789b
  1. .gitattributes
  2. README
  3. git-codereview/