USAGE description requires command while it isn't requirement

[CompuRoot]

gomtree -h

Returns:

USAGE:
   gomtree [global options] command [command options] [arguments...]

where command is required argument to gomtree while in fact there no functional commands (except help) that needed to run gomtree

Suggestion to get rid of : command [command options] at all since it isn't matched upstream and has no functionality in the gomtree

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Also, it might be good to add description (stolen from MTREE(8)) in help section:

DESCRIPTION
    The mtree utility compares the file hierarchy rooted in the current
    directory against a specification read from the standard input. Messages
    are written to the standard output for any files whose characteristics
    do not match the specification, or which are missing from either the
    file hierarchy or the specification.

[vbatts]

the "command" is expected. 17687d8 was done so that we could maintain the top-level compatibility, but also begin adding features in subcommands, for specific functionality.
Specifically I want to handle an ordered list of tars that are intended for container image layers, to produce or check that the resulting container image directory hierarchy #76

[vbatts]

I'll open a separate issue for the description.