Add style guide (#161)

Author: willtebbutt

README.md

@@ -5,6 +5,8 @@
 [![Documentation (stable)](https://img.shields.io/badge/docs-stable-blue.svg)](https://juliagaussianprocesses.github.io/KernelFunctions.jl)
 [![Documentation (latest)](https://img.shields.io/badge/docs-dev-blue.svg)](https://juliagaussianprocesses.github.io/KernelFunctions.jl/dev)
 [![ColPrac: Contributor's Guide on Collaborative Practices for Community Packages](https://img.shields.io/badge/ColPrac-Contributor's%20Guide-blueviolet)](https://github.com/SciML/ColPrac)
+[![Code Style: Blue](https://img.shields.io/badge/code%20style-blue-4495d1.svg)](https://github.com/invenia/BlueStyle)
+
 
 ## Kernel functions for machine learning