Documents Roll20's recent usage of simple-peer

[danielxvu]

What is the purpose of this pull request? (put an "X" next to item)

[x] Documentation update [ ] Bug fix [ ] New feature [ ] Other, please explain:

What changes did you make? (Give an overview)

The list of who's using simple-peer has been updated to include Roll20 per the new voice & video beta.

Which issue (if any) does this pull request address?

n/a

Is there anything you'd like reviewers to focus on?

n/a