CLI: Add help command

[jescalan]

It would be useful if there were a help or --help command that would print out usage instructions. Here is a tiny library I made for making these sorts of things easier 😀, if that helps at all!

[scottcorgan]

Great idea. On a branch for now, until we merge.

[ithinkihaveacat]

Did this actually get merged? There doesn't seem to be any way to actually trigger help, at least with version 6.0.4 (latest as of today):

❯ superstatic help

Superstatic started.
Visit http://localhost:3474 to view your app.
^C⏎                                                                                                 
~
❯ superstatic --help

Superstatic started.
Visit http://localhost:3474 to view your app.
^C⏎                                                                                                 
~
❯ superstatic -h

Superstatic started.
Visit http://localhost:3474 to view your app.
^C⏎                                                                                                 
~