git-codereview: fix references to 'git review' in doc.

There were 4 places where the doc mentioned 'git review'.
These should be 'git codereview'.

Change-Id: I335e182ff3316b813813dec9ac3b6702a2c02e82
Reviewed-on: https://go-review.googlesource.com/3670
Reviewed-by: Minux Ma <minux@golang.org>
1 file changed
tree: bbca13ecb73a18a3c057e65a5e512ecc2b88f9fe
  1. .gitattributes
  2. README
  3. git-codereview/