QC: Update contributor guidelines

[lauramaxwell]

QC Details

Guidelines are a bit out of date. for example in Appendix 1, release checklist, we no longer have the need to perform this action:

After the version in the DESCRIPTION file is updated, run gsm::UpdateGSMVersion() to update metadata that includes the gsm version number.

There are likely other out-of-date guidelines to update here.

Additional Comments

[jwildfire]

Also probably a good time to move this out of vignette and in to the GitHub standard. Might even consider hosting this in OpenRBQM

cc: @jonthegeek

[jonthegeek]

I think it's still useful to have per-repo contributor guidelines, so we can give explicit instructions about setting things up, any specific guidelines for a particular package, etc. But we can definitely move them to .github/CONTRIBUTING.md during this update.

I'm holding off from taking assigning this issue to myself because I'm not confident that I know what's desired here 🙃