Update webrtc-direct blog post

[p-shahi]

The current webrtc-direct blog post contains wrong information: https://blog.libp2p.io/libp2p-webrtc-browser-to-server/
@2color pointed out

Wrong (or outdated?) multiaddr: https://blog.libp2p.io/libp2p-webrtc-browser-to-server/#multiaddress with webrtc rather than webrtc-direct
No mention of webrtc-direct (except for the old and deprecated webrtc-direct)