document running linter w/ test-bot

Maybe this should be obvious, but as a first time committer it took me a few
rounds of CI fails before I figured out how to get this check to run locally.

Author: rrotter

Diff for: README.md

@@ -92,6 +92,7 @@ Note: based on these criteria, we would not accept e.g. Whalebrew (but have no p
 ## Tests
 
 Tests can be run with `bundle install && bundle exec rspec`.
+Syntax linting can be run with `brew style homebrew/bundle`.
 
 ## Copyright