Document websocket proxy

[sinui0]

Recently there was confusion around the role/security implications of the websocket proxy we use for browser deployments. We should document it, particularly the fact that it does not see any unencrypted application data.

[themighty1]

While this can be documented in the Browser extension, we can also extract some of the stumbling blocks into the FAQ section. I'll open a new issue where we could list some things that deseve to be put in an FAQ section.

Edit: added to #24

[maceip]

#93