Code of conduct, contribution guide, etc. are not auto-detected by GitHub

[Bisaloo]

Because they use the .Rmd file extension that GitHub doesn't know about. GitHub expects a .md extension for these files.

Different fixes may be applied to different files:

• Code of conduct file should probably be deleted because it's handled at the organization-level
• Contributing guide should be reviewed and potentially renamed, or deleted
• Citation file should be updated to use CITATION.cff as now recommended in the Carpentries lessons. If I remember correctly, there will be a coordinated effort from the Carpentries core team here.