Create a "How to be a good participant" document

DRAFT: https://github.com/w3c/PWETF/wiki/(DRAFT)-How-to-be-a-Good-Participant (feel free to contribute to this page or provide comment in this issue). 

We should have a document outlining what it means to be a good participant, that can also be reused by chairs to provide group practices and norms and what it means to be a good participant in W3C and in a group specifically. 