Add 'How to use' instructions

[BlackstoneEngineering]

Problem

For someone unfamiliar with Eagle it is not clear how to use the libraries in the HDK. Ie are they required to add the libraries one by one, or copy / paste them into the eagle /lbr folder? ..etc

Solution

Add a short section in the readme on what the expected use flow for the HDK is. Need to provide a sensible default flow.