Update switch stream muxer doc

[yusefnapora]

I mentioned the switch / swarm in the transport doc, but a more in-depth look at the public API surface and its responsibilities would help clarify things for users.

Could include:

• discussion of peer store / peer book
• dialing / listening API methods (examples in go, js, rust)
• short example of dial / listen interaction flow
  • can link to related concept docs

related concept docs:

• connection upgrade
• protocol negotiation
• transport
• secure comms
• nat traversal