update member repo onboarding pages

[mbjones]

The website currently has a lightweight onboarding description here: https://www.dataone.org/jointhenetwork/

It points at an outdated onboarding description here: https://dataone-operations.readthedocs.io/en/latest/MN/deployment/mn_checklist.html

We need to update both of these with some better documentation of how to join the network. Let's include a basic overview of options for joining, such as:

• Use schema.org to harvest an existing catalog (e.g., from a GeoNetwork or CKAN catalog)
• Subscribe to our hosted repository service
• Deploy and maintain our open source repository software on your own hardware
  • Metacat
  • GMN
• Implement the DataONE API yourself