Provide usage instructions and callout forcing deep merge

Adding instructions about 1) how to install and save to package.json, 2) how to load lib (the example in your test directory is referencing ../lib and I imagine this will confuse people), and 3) explain that you must pass boolean true to force deep merge.

I will close my fork when this pull request is accepted.

Thanks for putting this plugin together! Also, the tests are both thorough and entertaining :-)