Add more operational info to server and client documentation

[masomel]

Provide more details about the server's and the client's capabilities, what an operator needs to do to get a server or a client set up and running, and security considerations. As Bryan put it, make the READMEs more like a "tutorial".

Here are some other concrete questions that we should explicitly address in our documentation:

• Is the operator of the server expected to create a new namespace, e.g., such that users sign up for a new “CONIKS identity” account?
• If so, how does the CONIKS server interact with the DNS namespace it lives it, what are the integration requirements with DNS and other institutional networks, etc?
• How do users request names in this namespace, how do names transfer ownership, etc.?
• Can users bring their existing (E-mail) identities, submit them to the CONIKS server for verification, and the CONIKS server does an E-mail challenge/response to that E-mail account before incorporating the attestation into its next Merkle tree?
• In this case, what challenge/response technologies are currently supported - E-mail? phone/sms?
• Which are on the roadmap for the future?