Add support for providing a TOTP key

[jakawell]

• Add ability to provide a TOTP secret key, with entrypoint generating the TOTP for each connection (rather than having to pass the actual key on startup)
• Some fixes to the Dockerfile for broken dependencies
• Add documentation for TOTP support

[wazum]

@jakawell looks great, I'll take a look at it. Since you removed a few lines that I thought were important when I first set up the project, I need to double-check all of this first before merging.

[jakawell]

@wazum Yeah definitely. I couldn't get it to work with those lines (DNS was broken), but let me know.