Can disable build bumping for a testflight deploys via config

We still check that the repo is clean but do not require it to be the head of origin/master as we don't need to commit anything.
[completes #55131540]
Updates readme to include notes on the increments_build_number configuration field.
[#55131540]
Merge pull request #6 from pivotalstrings/master

Disables build bumping during Testflight deployments via configuration