Add Gratipay Badge [ci skip]

Note: anyone on the GitHub Pillow Team interested in receiving donations for their contributions may do so via the Gratipay Pillow Team (https://gratipay.com/pillow/). I'm not sure how to add folks, but if you are interested I will figure it out (I'm currently the only recipient.)

README.rst

@@ -55,3 +55,11 @@ More Information
 - `Changelog <https://github.com/python-pillow/Pillow/blob/master/CHANGES.rst>`_
 
   - `Pre-fork <https://github.com/python-pillow/Pillow/blob/master/CHANGES.rst#pre-fork>`_
+
+.. raw:: html
+
+    <div style="float: right">
+        <a href="https://gratipay.com/pillow/">
+          <img alt="Support via Gratipay" src="https://cdn.rawgit.com/gratipay/gratipay-badge/2.3.0/dist/gratipay.png"/>
+        </a>
+    </div>

docs/index.rst

@@ -41,6 +41,12 @@ Pillow is the friendly PIL fork by `Alex Clark and Contributors <https://github.
    about.rst
    releasenotes/index.rst
 
+.. raw:: html
+
+    <a href="https://gratipay.com/aclark4life/">
+      <img alt="Support via Gratipay" src="https://cdn.rawgit.com/gratipay/gratipay-badge/2.3.0/dist/gratipay.png"/>
+    </a>
+
 Indices and tables
 ==================