The process for making a Third-Party CI voting needs docs

Currently the process for making a Third-Party CI system voting
is not documented. This patch documents the current ideal process
for moving a Third-Party CI system from the non-voting permissions
group to the voting permissions group in Gerrit.

Change-Id: I762aec397f1c0c26bab62fbcb124e8b002066a43
Merge "The process for making a Third-Party CI voting needs docs"