[BUG] Document how to install pre-commit

[stevepiercy]

Describe the bug

There's no installation instructions for pre-commit in the documentation. It should go after https://icalendar.readthedocs.io/en/latest/contribute/development.html#install-tox.

See mentions in:

• Documentation contribution guide improvement ideas #991
• Add RFC 9253 compatibility #941 (comment)