First-time contributors guide

[stevepiercy]

From the discussion at #927, we ought to provide some guidance to first-time contributes to be successful and avoid spam and AI slop.

See comment at #927 (reply in thread) for sample content.

• Create first-time contributors documentation.
• Add configuration or sign up for programs that encourage first-time contributions, including the following.
  • Hacktoberfest. See https://hacktoberfest.com/participation/#pr-mr-details.
  • Good First Issue. See https://github.com/DeepSourceCorp/good-first-issue#adding-a-new-project.
  • Up For Grabs. See https://github.com/up-for-grabs/up-for-grabs.net/blob/gh-pages/docs/list-a-project.md.

We should not duplicate the documentation of how to participate in each program, as it may change and would be a maintenance headache.

[SashankBhamidi]

+1

[niccokunzmann]

Adding us to Good First Issue: DeepSourceCorp/good-first-issue#2450. Needed to adjust CONTRIBUTING.md in #939.

[niccokunzmann]

Created up-for-grabs/up-for-grabs.net#5409, so we should be listed as soon as possible on all three sites.

I would add it here: https://icalendar.readthedocs.io/en/latest/contribute/
Below "Examples of how to contribute"