Documentation: make the `cb help` command show specific help for specific commands

[MaddyGuthridge]

Currently, cb help shows a generic help message, regardless of later arguments.

$ cb help
# ...Generic help
$ cb help cp
# ...The same generic help

While the help is very detailed, because it is generic, it means that users need to sift through it to find the bit of information they need.

The way I would make it work would be:

$ cb help
# ...Generic help
$ cb help copy
# Info about the copy command
$ cb help cp1
# Info about the copy command, but also specifically saying how `cb` interpreted the command. Eg:
Clipboard will copy the given text to clipboard #1

In particular, since cb has lots of aliases, a simple explanation of how the alias given to the cb help command is interpreted would be super useful for helping new users understand how it works.

Thanks, as always, for your hard work on this project! I cannot stress enough how much I love having a consistent method for terminal clipboard management across all of my systems.