CODECONVENTIONS: Update for change from black to ruff format.

Also add notes on running pre-commit manually.

Signed-off-by: Andrew Leech <andrew@alelec.net>

CODECONVENTIONS.md

@@ -53,13 +53,16 @@ are then certifying and signing off against the following:
 Code auto-formatting
 ====================
 
-Both C and Python code are auto-formatted using the `tools/codeformat.py`
-script.  This uses [uncrustify](https://github.com/uncrustify/uncrustify) to
-format C code and [black](https://github.com/psf/black) to format Python code.
-After making changes, and before committing, run this tool to reformat your
-changes to the correct style.  Without arguments this tool will reformat all
-source code (and may take some time to run).  Otherwise pass as arguments to
-the tool the files that changed and it will only reformat those.
+Both C and Python code formatting are controlled for consistency across the
+MicroPython codebase.  C code is formatted using the `tools/codeformat.py`
+script which uses [uncrustify](https://github.com/uncrustify/uncrustify).
+Python code is linted and formatted using
+[ruff & ruff format](https://github.com/astral-sh/ruff).
+After making changes, and before committing, run  `tools/codeformat.py` to
+reformat your C code and `ruff format` for any Python code.  Without
+arguments this tool will reformat all source code (and may take some time
+to run).  Otherwise pass as arguments to the tool the files that changed,
+and it will only reformat those.
 
 uncrustify
 ==========
@@ -151,12 +154,22 @@ Tips:
 * To ignore the pre-commit message format check temporarily, start the commit
   message subject line with "WIP" (for "Work In Progress").
 
+Running pre-commit manually
+===========================
+
+Once pre-commit is installed as per the previous section it can be manually
+run against the MicroPython python codebase to update file formatting on
+demand, with either:
+* `pre-commit run --all-files` to fix all files in the MicroPython codebase
+* `pre-commit run --file ./path/to/my/file` to fix just one file
+* `pre-commit run --file ./path/to/my/folder/*` to fix just one folder
+
 Python code conventions
 =======================
 
 Python code follows [PEP 8](https://legacy.python.org/dev/peps/pep-0008/) and
-is auto-formatted using [black](https://github.com/psf/black) with a line-length
-of 99 characters.
+is auto-formatted using [ruff format](https://docs.astral.sh/ruff/formatter)
+with a line-length of 99 characters.
 
 Naming conventions:
 - Module names are short and all lowercase; eg pyb, stm.