[mediacapture-fromelement] Describe what track attributes are set to

stefhak has just created a new issue for 
https://github.com/w3c/mediacapture-fromelement:

== Describe what track attributes are set to ==
The spec says nothing about what MediaStreamTrack attributes such as 
kind, label, readonly, remote should be set to.
While apparent in some cases, this should be documented.

Please view or discuss this issue at 
https://github.com/w3c/mediacapture-fromelement/issues/32 using your 
GitHub account