add 'back on patreon' shields.io button (#303)

README.md

@@ -5,6 +5,7 @@
 [![Twitter](https://img.shields.io/twitter/url/https/twitter.com/fold_left.svg?style=social&label=Follow%20%40AlgoVPN)](https://twitter.com/AlgoVPN)
 [![Flattr](https://button.flattr.com/flattr-badge-large.png)](https://flattr.com/submit/auto?fid=kxw60j&url=https%3A%2F%2Fgithub.com%2Ftrailofbits%2Falgo)
 [![PayPal](https://www.paypalobjects.com/en_US/i/btn/btn_donate_SM.gif)](https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=CYZZD39GXUJ3E)
+[![Patreon](https://img.shields.io/badge/back_on-patreon-red.svg)](https://www.patreon.com/algovpn)
 
 Algo VPN is a set of Ansible scripts that simplifies the setup of a personal IPSEC VPN. It contains the most secure defaults available, works with common cloud providers, and does not require client software on most devices.