Onboarding docs

[rbowen]

Per-persona (packager, dev, docs) onboarding document. Use https://fedoraproject.org/wiki/Join as inspiration for the kind of thing that we're going for.

[pmkovar]

• I guess there should be a prominent link pointing to this page directly from the front page?
• For developer resources, we would probably just link to individual upstream project contributor pages?

[amoralej]

I've added a simple onboarding guide for packagers as part of #952

[snecklifter]

@rbowen onboarding worked well for me so I guess this can be closed now?

[pmkovar]

I think so. https://www.rdoproject.org/documentation/onboarding/ is linked from https://www.rdoproject.org/contribute/ which now features personas.

[pmkovar]

The only remaining task here being moving devel docs under contribute/, but that's part of a bigger task.