Add Patreon badge and link

Fixes #15

README.md

@@ -1,4 +1,5 @@
 # vuex-map-fields
+[![Patreon](https://img.shields.io/badge/patreon-donate-blue.svg)](https://www.patreon.com/maoberlehner)
 [![Donate](https://img.shields.io/badge/Donate-PayPal-blue.svg)](https://paypal.me/maoberlehner)
 [![Build Status](https://travis-ci.org/maoberlehner/vuex-map-fields.svg?branch=master)](https://travis-ci.org/maoberlehner/vuex-map-fields)
 [![Coverage Status](https://coveralls.io/repos/github/maoberlehner/vuex-map-fields/badge.svg?branch=master)](https://coveralls.io/github/maoberlehner/vuex-map-fields?branch=master)
@@ -441,7 +442,8 @@ export default new Vuex.Store({
 Markus Oberlehner  
 Website: https://markus.oberlehner.net  
 Twitter: https://twitter.com/MaOberlehner  
-PayPal.me: https://paypal.me/maoberlehner
+PayPal.me: https://paypal.me/maoberlehner  
+Patreon: https://www.patreon.com/maoberlehner
 
 ### License
 MIT