Updates to CONTRIBUTING.md for the modern gerrit era.
Updates to CONTRIBUTING.md for the modern gerrit era.

Change-Id: I5cb5f08e2086078d041f1d1aac154b6e43428907
Reviewed-on: http://review.couchbase.org/119171
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Sergey Avseyev <87f6d5e4fd3644c3c20800cde7fd3ad1569370b3@gmail.com>

couchbase/libcouchbase,couchbase/libcouchbase,couchbase/libcouchbase,couchbase/libcouchbase,kojiromike/libcouchbase,couchbase/libcouchbase,kojiromike/libcouchbase,couchbase/libcouchbase,couchbase/libcouchbase,kojiromike/libcouchbase,kojiromike/libcouchbase