Added a note about `git diff --check` for whitespace linting.
|@@ -317,6 +317,7 @@ follows:|
|* Do your best to adhere to the existing coding conventions and idioms.|
|* Don't use hard tabs, and don't leave trailing whitespace on any line.|
|+ Before committing, run `git diff --check` to make sure of this.|
|* Do document every method you add using [YARD] annotations. Read the|
|[tutorial][YARD-GS] or just look at the existing code for examples.|
|* Don't touch the `.gemspec` or `VERSION` files. If you need to change them,|