update README

README.md

@@ -2,3 +2,12 @@
 
 [![Build Status](https://travis-ci.org/JuliaDiff/DiffBase.jl.svg?branch=master)](https://travis-ci.org/JuliaDiff/DiffBase.jl)
 [![Coverage Status](https://coveralls.io/repos/github/JuliaDiff/DiffBase.jl/badge.svg?branch=master)](https://coveralls.io/github/JuliaDiff/DiffBase.jl?branch=master)
+
+**[Go to DiffBase's Documentation](http://www.juliadiff.org/DiffBase.jl/)**
+
+DiffBase is a Julia package that provides common utilities and test functions that are used
+by various JuliaDiff packages.
+
+If you're a user of any JuliaDiff packages, you may want to check out DiffBase's [DiffResult
+API](http://www.juliadiff.org/DiffBase.jl/diffresult/), which can be used in conjunction
+with other packages in order to compute multiple orders of derivatives simultaneously.