Documentation for pre-commit hook needs updating

[peetw]

The documentation for the pre-commit hook (added in #35) currently states that rev: v0.2.9 should be used. However, the pre-commit hook was added after the v0.2.9 tag, which means that pre-commit fails to install the hook (since .pre-commit-hooks.yaml doesn't exist in the repo for tag v0.2.9).

Therefore, the documentation needs to be updated to point to either a new tag for the most recent version of the code (e.g. rev: v0.2.10) or the latest commit SHA (i.e. rev: 5fb3ce7).