Issue #63 Interoperability created

Dear all,

while I was checking issue #61, I stumbled across a todo that was not 
yet addressed.

Interoperability:

  * How to Discover it (Where is it? Who produces it?)
  * How to Interact with it (What format is it, etc.)

I created https://github.com/w3c/voiceinteraction/issues/63 
Interoperability out of that.

Debbie, I think that this one originates from you. Do you have any idea 
how this could be handled? Others are of course also invited to comment.

Dirk