Copy Editing Suggestions

Here are some suggestions for editing this markdown. Other than some basic copy editing, here were some larger changes I suggested

Some content explaining the difference between RSpec and MiniTest - I remember being confused about this for a while

A note on working from the main directory

A link to the comparable mixin info - I was a little confused on the first read about why you brought up the comparable mixin if we weren't going to use it. 

An explanation on attr_reader vs. attr_accessor and recognizing which to use from the test failure

Running rake before adding a rake file, to show that ruby knows about the 'rake' command already