Log warning when using default ICE servers

I‘ve seen quite a few issues here and people asking online why their connection doesn‘t seem to go past signaling and fails. Oftentimes under specific circumstances, like only with one browser or one network.

I had the same issue over the weekend with the combination Firefox <-> iOS Safari, both in a local network and via internet in various combinations. I was debugging for hours until I found the solution: *You have to use your own ICE servers*.
In hindsight this seems so obvious, since the default values for iceServers are servers that aren‘t really public. What makes it worse is that it does seem to work _sometimes_. In the case of the server hosted by Google it was only working when at least one of the devices was Chrome.

Signing up at Twilio and generating a few URLs with credentials for their STUN/TURN servers took me less than 10 minutes and suddenly I was able to connect any device in any configuration in any network.

I just thought I‘d put this here for others experiencing the same issue. And I was wondering, maybe it would make sense to highlight this fact a bit more in the readme?
It was not directly obvious to me, only after I read a bit more about WebRTC in general. It‘s a classic case of RTFM, but it seems the "M" here is a bit scattered around the internet :)