Add README sections referencing Community Health files

[MJJoyce]

We added default community health files to NASA-PDS/.github to provide all repositories in our Org with sane defaults for critical files. Unfortunately, the visibility of these default files is less than ideal. See NASA-PDS/.github#7 for the original motivation for this ticket, including screenshots demonstrating potential "issues" with the visibility of these defaults.

We should add a sections to our template README that provides links to these default files to increase visibility.

Direct links:
Code of Conduct
Contributing