added docs for assisted teleop behavior and bt node

[jwallace42]

No description provided.

[SteveMacenski]

Also migration guide (actually, make a new migration guide page for Humble -> Iron since this won't get in before the Humble branch) page and a quick tutorial would be amazing. The tutorial should cover:

• How to add to the behavior plugins list in yaml
• How to add to a BT
• Showing how it works in a video
• Maybe a quick diagram about how it works internally, if you feel it helps in the explanation

[SteveMacenski]

A tutorial for use would be ideal, but not strictly required