Adds Github recommended supporting docs

[eidolonnight]

This adds code_of_conduct.md, contributing.md, and support.md files to the Marketing Team repo. These are recommended pages outlined under the Building communities Github documentation, and these should aid in directing new contributors to various resources. Links appear in various places within the team repository, including the sidebar when submitting new issues.

This initial commit creates basic pages with links to the handbook and other resources.

[eidolonnight]

This pull request is the first half of work toward https://github.com/WordPress/Marketing-Team/issues/140

[sereedmedia]

Hi, thanks for tagging me! My comments:

• There is an existing WordPress Code of Conduct. I am not okay with the Marketing Team adopting a unique Code of Conduct. Emphasis for emphasis. That is not something that can be maintained or enforced properly by the Marketing Team. Any Code of Conduct referenced or developed should apply project-wide. If we feel that we need a more specific Code of Conduct for contribution than what is covered in the existing WordPress Code of Conduct, then that is something we should bring up with the Community Team or discuss in the Team Reps channel.
• The handbook link in Support resources is not linking properly.
• I think linking back to the official WordPress.org site and marketing team handbook as you have done with the contributing and support pages is the best way to handle all of these docs, including (especially) the Code of Conduct. AFAIK, the Make Team Handbooks are currently the "single source of truth" for WordPress contribution.

[sereedmedia]

Did an official review, but the same comments as my original. Redundancy is good for everyone and everybody!

[sereedmedia]

@jpantani can you review so we can get this closed and posted? it's super basic content.