Community health files for the EESSI organization

• The README.md in the profile folder controls the contents of https://github.com/EESSI
• The top-level *.md files (except README.md) are picked up in each repository under the EESSI organization (see for example Security tab).

For more information, see https://help.github.com/en/articles/creating-a-default-community-health-file-for-your-organization