Update Auth Extension doc
Update Auth Extension doc

Move configuration info up as it needs to be done first, add info about
supported client types. Cleanup.

https://trello.com/c/Jwm0YHzE/857-auth0-authorization-extension
https://trello.com/c/6iVST4nu/716-auth0-authorization-extension

sandrinodimattia/docs,Annyv2/docs,jeffreylees/docs,auth0/docs,hamzawi06/docs,jeffreylees/docs,khorne3/docs,sandrinodimattia/docs,khorne3/docs,yvonnewilson/docs,yvonnewilson/docs,auth0/docs,auth0/docs,sandrinodimattia/docs,hamzawi06/docs,hamzawi06/docs,khorne3/docs,Annyv2/docs,yvonnewilson/docs,jeffreylees/docs,Annyv2/docs