Mention separate just autofix-* commands in CONTRIBUTING.md

Author: nathanjmcdougall

CONTRIBUTING.rst

@@ -122,7 +122,7 @@ Before you push
 
 It's a good idea to run ``just full-check`` before getting a review.
 This will run linters, docs build and tests under every supported Python version.
-You can automatically fix many lint errors using ``just autofix``.
+You can automatically fix many lint errors using ``just autofix`` (or ``just autofix-python`` and ``just autofix-rust`` separately).
 
 Benchmarking
 ============