Issue title: Missing installation instruction
 Issue body: Would be nice if there was a short instruction how to install this plugin. I really have no idea how to bring this to life :(

 Comments: 
 Comment 0: Can be installed via NPM or Bower (once the 1.2.0 version is published to NPM and Bower).
Can also be used in the browser.

See https://github.com/jsmreese/moment-duration-format#installation

 Comment 1: Thanks for this. The most important for me was to include lodash.js or underscore.js :D

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