Update contribution guidelines wrt pre-commit hook #5201
Description
What
We should update the contributor guidelines to point external contributors to use the devtool instead of the current "local" pre-commit hook setup.
Why
The pre-commit hook is unmaintained, unused by the team, and currently doesn't work if the setup is different from the devctr (see #5180).
How
The equivalent operation in the devtool is ./tools/devtool fmt.
Other information
We should keep the git-secrets check, moving it to the devtool if it's not already there.