Description:
    Creates a Completions file.
    The most basic form of adding completions to Sublime Text is by creating a .sublime-completions file. Completions files use the JSON format, and contain an object with the keys "scope" and "completions".

    See: http://www.sublimetext.com/docs/completions.html#completion-files

Example:
    yo sublime-package:completion

    This will create:
        completions/SublimePackage.sublime-completions:                  Completion files are smart templates that will insert text for you, adapting it to their context.

