contributions info

[naughtont3]

Create contributions file and a separate contribs subdir that is all in MD and not to be rendered on www page. The intent is to house details for contributions and consistent formatting, useful "author" info, procedures for publishing docs, etc.

[naughtont3]

Use maint/ dirname

[naughtont3]

See:

• https://docs.github.com/en/communities/setting-up-your-project-for-healthy-contributions/setting-guidelines-for-repository-contributors
• https://contributing.md/how-to-build-contributing-md/