Python version and pre-commit

.pre-commit-config.yaml

@@ -0,0 +1,14 @@
+repos:
+-   repo: local
+    hooks:
+    -   id: codeformat_c
+        name: codeformat-c
+        language: system
+        entry: poetry run ./tools/codeformat.py -cf
+        types: [c]
+    -   id: codeformat_py
+        name: codeformat-py
+        language: system
+        entry: poetry run ./tools/codeformat.py -p
+        types: [python]
+        pass_filenames: false

CONTRIBUTING.md

@@ -215,6 +215,16 @@ Before committing your changes, be sure to run:
 This will automatically fix common problems in files that follow the MicroPython
 style.
 
+This can be run automatically before making a commit using [pre-commit][]. To
+enable it, run:
+
+    poetry run pre-commit install
+
+It will install a pre-commit git hook for this repository. On every commit,
+the coding style will be checked and fixed before the commit is done.
+
+[pre-commit]: https://pre-commit.com/
+
 
 ### Logical commits