Update README.md

Author: andreasrosdal

README.md

@@ -3,7 +3,7 @@
 OpenPDF5 is an open source library for PDF files, maintained in accordance with the AGPL license. OpenPDF5 is a maintained fork of iText 5, and is licensed as [AGPL][agpl] software.
 
 
-[![Join the chat at https://gitter.im/LibrePDF/OpenPDF](https://badges.gitter.im/LibrePDF/OpenPDF.svg)](https://gitter.im/LibrePDF/OpenPDF) [![Build Status](https://travis-ci.org/LibrePDF/OpenPDF5.svg?branch=develop)](https://travis-ci.org/LibrePDF/OpenPDF5)  [![License: AGPL v3](https://img.shields.io/badge/License-AGPL%20v3-blue.svg)](https://www.gnu.org/licenses/agpl-3.0)
+<a href="https://patreon.com/openpdf" title="Donate to this project using Patreon"><img src="https://img.shields.io/badge/patreon-donate-green.svg" alt="Patreon donate button" /></a> [![Join the chat at https://gitter.im/LibrePDF/OpenPDF](https://badges.gitter.im/LibrePDF/OpenPDF.svg)](https://gitter.im/LibrePDF/OpenPDF) [![Build Status](https://travis-ci.org/LibrePDF/OpenPDF5.svg?branch=develop)](https://travis-ci.org/LibrePDF/OpenPDF5)  [![License: AGPL v3](https://img.shields.io/badge/License-AGPL%20v3-blue.svg)](https://www.gnu.org/licenses/agpl-3.0)
 
 
 ## Contributing ##