Improves the documentation of the webrtc crate

[kenaniah]

Hi all. My company is in the process of building a product on top of this project, and we are looking to become regular contributors to the webrtc-rs ecosystem. As a start, we would like to contribute a baseline set of documentation to the webrtc crate.

Although this effort is still underway, I wanted to open up a draft PR to surface the work that we are doing on this front, in the hopes of getting early feedback from the maintainers & the community, in the hopes that this will be the first of many contributions back to upstream that we make.

WebRTC Crate Documentation

• Crate overview
• RTCConfiguration
• RTCIceServer
• RTCIceTransportPolicy
• RTCBundlePolicy
• RTCRtcpMuxPolicy
• RTCSignalingState
• RTCIceGatheringState
• RTCPeerConnectionState
• RTCIceConnectionState
• RTCPeerConnection
• RTCSdpType
• RTCSessionDescription
• RTCIceCandidate
• RTCIceProtocol
• RTCIceCandidateType
• RTCIceServerTransportProtocol
  ...

[codecov]

Codecov Report

Patch coverage: 42.85% and project coverage change: +0.01% 🎉

Comparison is base (71157ba) 61.51% compared to head (9ca2925) 61.52%.

❗ Current head 9ca2925 differs from pull request most recent head f9518b6. Consider uploading reports for the commit f9518b6 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #482      +/-   ##
==========================================
+ Coverage   61.51%   61.52%   +0.01%     
==========================================
  Files         529      530       +1     
  Lines       48839    48863      +24     
  Branches    12361    12352       -9     
==========================================
+ Hits        30043    30063      +20     
- Misses       9607     9617      +10     
+ Partials     9189     9183       -6     

Files Changed	Coverage Δ
interceptor/src/stats/interceptor.rs	79.05% <ø> (ø)
interceptor/src/stats/mod.rs	80.29% <ø> (-2.92%)	⬇️
webrtc/src/ice_transport/ice_gathering_state.rs	92.85% <ø> (ø)
webrtc/src/ice_transport/ice_server.rs	85.18% <ø> (ø)
webrtc/src/lib.rs	100.00% <ø> (ø)
webrtc/src/peer_connection/configuration.rs	94.11% <ø> (ø)
webrtc/src/peer_connection/offer_answer_options.rs	0.00% <ø> (ø)
...ebrtc/src/peer_connection/peer_connection_state.rs	65.78% <ø> (ø)
webrtc/src/peer_connection/policy/bundle_policy.rs	100.00% <ø> (ø)
...src/peer_connection/policy/ice_transport_policy.rs	69.23% <ø> (ø)
... and 3 more

... and 19 files with indirect coverage changes

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[rainliu]

@kenaniah , thank you for improving the documentation. This will greatly help people learn how to use webrtc-rs APIs.