Add note about WebRTC version to README (see #93)

README.md

@@ -1,3 +1,8 @@
+**If you do not have specific requirements, please consider using the `webrtc` version instead: https://github.com/Johni0702/mumble-web/tree/webrtc (note that setup instructions differ significantly).
+It should be near identical in features but less susceptible to performance issues. If you are having trouble with the `webrtc` version, please let us know.**
+
+PRs, unless webrtc-specific, should still target `master`.
+
 # mumble-web
 
 mumble-web is an HTML5 [Mumble] client for use in modern browsers.