Add Admin Info to Docs

[danloveg]

The documentation for the admin site is sparse right now. I would like these things to be added to the administrator docs:

• Adding users manually
• Managing bags (view metadata, set review status, etc.)
• Viewing bag groups
• Viewing jobs
• Managing site name (this is for superusers only)

There should be screenshots included so that people don't get bored of reading a wall of text.

[danloveg]

This is currently in progress. I have added info to the docs on:

• Adding users
• Adding rights taxonomies
• The transfer form
• Accepted file types
• Managing site name

I have decided to add Bag management to a separate section of the docs.