Cover troubleshooting steps/FAQs

[laurelmay]

There are a few typical scenarios that come up when this is run. We should document common failures and then try to provide solutions (or at least general context). Some starters:

• "What does 'BECOME password' mean?"
• "What's this bit about not being able to resolve ?"
• Apt operations failing
  • (Usually, btw, this is network connectivity; but it may be a previous failed transaction holding the lock file...)