message: Add note on dependency-update PRs to the contributor guidelines.
diff: @@ -8,6 +8,12 @@ Issues, ideas, requests and questions should be posted on the issue tracker at:
  https://github.com/japaric/criterion.rs/issues
  +## A Note on Dependency Updates
  +
  +Criterion.<span></span>rs does not accept pull requests to update dependencies unless specifically
  +requested by the maintaner(s). Dependencies are updated manually by the maintainer(s) before each
  +new release.
  +
  ## Code
  Pull requests are welcome, though please raise an issue for discussion first if none exists. We're happy to assist new contributors.
  