Provide manual page / command completion

[Jakuje]

When I need to make a cleanup, I always have to head here to the bottom of the README to find out what the command is.

It would help to have manual page or at least short usage of internal plugins hinting what arguments can be used. Even better to have bash-completion for the embedded plugins.

[t184256]

@shiragaki0 has added outputting usage examples in #28, narrowing this issue down to a manpage / command completion.