add donation badge

Author: willforde

README.rst

@@ -13,6 +13,9 @@
 .. image:: https://api.codacy.com/project/badge/Grade/6b46406e1aa24b95947b3da6c09a4ab5
     :target: https://www.codacy.com/app/willforde/python-htmlement?utm_source=github.com&utm_medium=referral&utm_content=willforde/python-htmlement&utm_campaign=Badge_Grade
 
+.. image:: https://img.shields.io/badge/Donate-PayPal-green.svg
+    :target: https://www.paypal.com/cgi-bin/webscr?cmd=_donations&business=SLQMJBWX7G2PU
+
 Installation
 ------------
 ::