[README.md] add description

Author: chrissimpkins

README.md

@@ -1,7 +1,7 @@
 <img src="https://raw.githubusercontent.com/source-foundry/fdiff/img/img/fdiff_logo-crunch.png" width="200" />
 <br/>
 
-
+## An OpenType table diff tool for fonts
 
 [![Build Status](https://travis-ci.org/source-foundry/fdiff.svg?branch=master)](https://travis-ci.org/source-foundry/fdiff)
 [![Build status](https://ci.appveyor.com/api/projects/status/eafvbkc4iyv78dip/branch/master?svg=true)](https://ci.appveyor.com/project/chrissimpkins/fdiff/branch/master)