git-review: add documentation

This is just the first draft.
We may need to add more, particularly to the intro.

Change-Id: Ia96d944c7867c8cecfe4476fa54f7d2a434c625d
Reviewed-on: https://go-review.googlesource.com/1703
Reviewed-by: Rob Pike <r@golang.org>
1 file changed
tree: 179d7a9c5dc1ae9697dbd217fda181ee66250266
  1. README
  2. git-review/