Handbook update with notes for using Gitlab team accounts with accountless...

I ran into a couple oddities setting up my Gitlab account with 1Password, so I made notes and have added some warnings to others that opt for this. I talked with 1Password support to verify the Master Password access rules, and am still clarifying a few things with them about how and/or why it works that way. If I come across more useful information, I'll add it here. But for now these are the practicalities to keep in mind.