WMF staff developer creation process updates
This commit:
- Adds .coverage to .gitignore
- Makes a small update to README.md about script usage
- Adds a new dev dependency to pyproject.toml
- Updates poetry.lock per ^
- Adds an updated includes/wmf_staff.csv file
- Adds the gen_wmf_git_users.py script to generate the wmf_staff.csv file (formerly not included in this repo)
- Adds a unit test for the gen_wmf_git_users.py script
Bug: T345447