Update README.md

- 1st screen device(chromacast) acts like proxy between two browser/app sessions 
- 2nd screen device creates app, then waits for connectionSvcURL
- 1st screen device after app starts issues REGISTER RAMP packet
- 1st > 2nd Issues CHANNELREQUEST with URL which is the same as that in connectionSvcURL in DIAL xml
- 2nd screen device connects via websockets using connectionSvcURL and isses LOAD, INFO, PLAY, STOP, VOLUME and other commands
- 1st screen responds accordingly