Add an `intro` command

[da2x]

I’d like to see a intro command (at the top of the help command list) that explains the basics dos and don’ts and links off to more documentation. A Hyper* toolset 101.

There’s a lot you should know about append-only file systems (e.g. issue #44), networking (do I need to worry about firewalls and port-forwarding), sharing-privacy (only people with the public key can access it, its protected in discovery), where are files stored and what the FUSE thing/folder is, privacy keys, important directories (for backing up), hyperswarm (peer discovery etc.), etc. before you can use Hyperdrive with confidence.