reword mpc_tls - Githubissues

This PR rewords the MPC-TLS section:

disambiguate that it is the Prover who connects to the server
remove the mention of a Notary to not distract from the more important Prover<->Verifier paradigm
change "verifier sees" to "verifier learns", otherwise it sounds like the verifier is MITMing.
remove mention of Transcript since it is better to introduce it in the deeper sections of the docs
added one more key point

tlsnotary / docs-mdbook