Overhaul the "Volunteer as a Mentor" section

[RichardLitt]

I think I know what I was doing with this, but it hasn't been used by anyone else. This is most likely because 1) we haven't mentioned it 2) the process isn't clear. I think a combination of both.

Integrating this with the website is probably the best way forward. This ticket exists to mention that we need to add a mentor userflow to the website.