Linux usage like help

The question is: how to add a usage, linux-like, to cmake file?

I have a lot of variables in my cmake files. I added Usage in the begining of the main cmake file, like this:
message( … )
message( … )
unset( USAGE CACHE )

And then when I run cmake, and want to get the usage message, I run it like this:
cmake -DUSAGE=TRUE <path/to/source>

And I get the usage messages

Is there a better option, builtin option or something else?

Asking the same question in other words:
How do I communicate my cmake users how to configure the project?

The recommend pattern is to use option for binary options. This way users that are using ccache or cmake-gui can also easily modify the state of the option.