• Previously the "note" would be treated as a comment (it needs two
  end colons); we can just make it plain text anyways.
• Moving the doc for the parameters to __init__ avoids __init__
  inheriting the docstring of the parent Rectangle.__init__ and thus
  the rendered docs getting two copies of the parameter list, with only
  one being correct.

See https://matplotlib.org/api/table_api.html#matplotlib.table.Cell.

PR Summary

PR Checklist

• Has Pytest style unit tests
• Code is Flake 8 compliant
• New features are documented, with examples if plot related
• Documentation is sphinx and numpydoc compliant
• Added an entry to doc/users/next_whats_new/ if major new feature (follow instructions in README.rst there)
• Documented in doc/api/api_changes.rst if API changed in a backward-incompatible way