Add contributing guide
For now, the DORiE repository will be made public, but contribution via GitLab is only possible as member of the TS-CCEES group. This has to be made clear in the contribution guide. Moreover, we have to address other ways of contributing.
- Indicate that GitLab accounts are only available for group members and associates
- Bug reports, feature requests, and improvement suggestions can be filed via email
- Indicate that resources for support are stretched thin within our group
- Discuss with @yunus (& Kurt?): Would we grant an account to external people willing to contribute to DORiE?