message: Add Branches section to contributing.md
diff: @@ -55,6 +55,15 @@ Some things that will increase the chance that your pull request is accepted:
  * Clearly document public methods
  * Write a good commit message
  +## Branches
  +
  +* PRs with breaking changes are made against the unreleased branch. e.g. branch version-0.4
  +* PRs without breaking changes are made against the master branch.
  +
  +If your not sure which branch to use just start with master, as this can be changed during review.
  +
  +When it is time to release the unreleased branch, a PR is made from the unreleased branch to master. e.g. https://github.com/bheisler/criterion.rs/pull/496
  +
  ## Github Labels
  Criterion.<span></span>rs uses a simple set of labels to track issues. Most important are the
  