Update CONTRIBUTING.md

Author: chester-leung

CONTRIBUTING.md

@@ -14,4 +14,4 @@ You can ask questions, bring up issues, or garner feedback through the following
    harder to merge in a large change with a lot of disjoint features.
 2. Submit the patch as a GitHub pull request against the master branch.
 3. Make sure that your code passes the automated tests.
-4. Make sure that your code passes the linter. Run `pip3 install pre-commit; pre-commit install` to create a git hook that will run the linter before you push your changes.
+4. Run `pip3 install pre-commit; pre-commit install` to create a git hook that will run the linter and automatically format your code when you commit. If the hook reformats your code, you'll need to `git add` the changed files again.