Catch-all for non-commands displaying --help

[paulstatezny]

Thanks for evm @mattludwigs! 😄

I gave a cursory glance at commander but I couldn't determine how to do it.

My thought is, mis-types like:

$ evm lms
$ evm insrall

would result in the help text:

  Usage: evm [options] [command]

  Commands:

    install|i <version>  installs version
    list|ls              lists out versions installed
    remove|rm <version>  removes a version that is installed
    use <version>        Sets up system to use a certain version of elm
    list-remote|lsrm     Lists the possible versions to download from
    remove-all|rma       removes all of your Elm versions

  Options:

    -h, --help     output usage information
    -V, --version  output the version number

Right now it just exits with no helpful feedback.

[paulstatezny]

Figured it out! Closing this in favor of #8.