[webrtc-pc] Pull Request: intro: increase scope to general p2p

fippo has just submitted a new pull request for https://github.com/w3c/webrtc-pc:

== intro: increase scope to general p2p ==
increases the scope in the intro beyond video conferencing.

fixes #1185

@burnburn please take a look

See https://github.com/w3c/webrtc-pc/pull/1221