Missing CONTRIBUTING.md document

[chrisfosterelli]

The README mentions:

to learn more about the group's structure and CONTRIBUTING.md for guidance
about the expectations for all contributors to this project.

But the link doesn't go anywhere, and the project doesn't appear to have a CONTRIBUTING.md document.

[chrisfosterelli]

I can create a PR to remove this from the README if you'd like! However I left this as an issue since I figured you may want to create an actual CONTRIBUTING.md document instead of removing it from the README.

[chorrell]

Yeah, we should probably have a CONTRIBUTING.md doc. It would be useful to have that to explain the process for how the images are updated and then updated in the Docker hub. That comes up a lot since people assume it's automatic and don't know we have to do a manual PR

[LaurentGoderre]

Closing since the file exists now