prplfoundation
documentation: Adapt CONTRIBUTING.md for the move to gitlab
This is an attempt at keeping the docs up to date with the move from github to gitlab. Since this document will be used as a template for prplWrt as well, it's double important that it stays up to date.
I anticipate we'll need another update once the move is complete and we've settled on how to work effectively with gitlab a bit more. The "Merge request workflow" in particular might change significantly, but I don't want to do it yet because I'm not certain yet what it will look like. Also, I don't know how (if) the DCO check still works with gitlab, or if we need to tweak things a little there. No doubt we'll discover other issues.
So, this is just an initial version of the contribution guidelines, adapted for gitlab.
See PPM-335
Before anyone comments: yes, there's some fixes related to JIRA and Confluence as well in here.
I didn't feel the need to do it in a separate PR or commit, since these are just small documentation fixes.