add new committer vote language to governance doc

Signed-off-by: Michael Robinson <merobi@gmail.com>

GOVERNANCE.md

@@ -69,8 +69,7 @@ This includes:
 New committers are voted onto the committers list by the existing committers. For the current list, see:
 [COMMITTERS.md](COMMITTERS.md).
 
-The committers vote, and if a majority agree then the requester
-is added to the committers list and given write access to the Git repositories.
+The committers vote; if there are at least 3 votes in support of the nominee and no vetoes in a period of three days, the nominee is added to the committers list and given write access to the git repositories.
 
 Once confirmed, you can publicly refer to yourself as a Marquez committer.