Add documentation for janus-gateway

Relates to #74

janus-gateway/README.md

@@ -0,0 +1,23 @@
+# janus-gateway
+janus-gateway is a collection of examples showing how to use pion-WebRTC with [janus-gateway](https://github.com/meetecho/janus-gateway)
+
+These examples require that you build+enable websockets with Janus
+
+## streaming
+This example demonstrates how to download a video from a Janus streaming room. Before you run this example, you need to run `plugins/streams/test_gstreamer_1.sh` from Janus.
+
+You should confirm that you can successfully watch `Opus/VP8 live stream coming from gstreamer (live)` in the stream demo web UI
+
+### Running
+run `main.go` in `github.com/pions/webrtc/examples/janus-gateway/streaming`
+
+If this worked you will see the following.
+```
+Connection State has changed Checking
+Connection State has changed Connected
+Got VP8 track, saving to disk as output.ivf
+```
+Currently pion-WebRTC doesn't implement DTLS retransmissions so audio/video may not start successfully, and Janus will timeout with a DTLS error. Issue [#175](https://github.com/pions/webrtc/issues/175) is tracking this.
+If video does start in under 3 seconds stop and start the example again, this may take a few tries.
+
+If video did start successfully you will see output.ivf in the current folder.