update readme, add gitter.
update readme, add gitter.

ossrs/srs,ossrs/srs,avplus/srs,avplus/srs,tribbiani/srs,tribbiani/srs,avplus/srs,winlinvip/srs,tribbiani/srs,antonioparisi/srs,ossrs/srs,antonioparisi/srs,lewdon/srs,winlinvip/srs,lewdon/srs,antonioparisi/srs,tribbiani/srs,lewdon/srs,avplus/srs,winlinvip/srs,lewdon/srs,winlinvip/srs,avplus/srs,winlinvip/srs,tribbiani/srs,winlinvip/simple-rtmp-server,antonioparisi/srs,lewdon/srs,ossrs/srs,ossrs/srs,lewdon/srs,antonioparisi/srs,antonioparisi/srs,avplus/srs,tribbiani/srs,avplus/srs,winlinvip/srs,tribbiani/srs,ossrs/srs