Update instructor notes

[ehogan]

Helper feedback from the Introduction to Git and GitHub training on Wednesday, January 29, 2025:

Describe what it means to be an instructor and a helper, and how they will interact with each other and the learners during the training.

This should be agreed by the instructor and the helper before the training.

For example, if I were an instructor, I would be more than happy for a helper to jump in if they have something useful to share / if I have forgotten something. The learners should be told about this, so that it doesn't appear to the learners that the helper is interrupting.