Adds donation link to docs

docs/.templates/sidebarintro.html

@@ -1,4 +1,15 @@
 <p class="logo"><a href="{{ pathto(master_doc) }}">
   <img class="logo" src="http://cloud.github.com/downloads/celery/celery/celery_128.png" alt="Logo"/>
 </a></p>
-
+<div id="donate">
+    <b>Please donate:</b>
+    <form id="paypal_donate" action="https://www.paypal.com/cgi-bin/webscr" method="post">
+        <input type="hidden" name="cmd" value="_s-xclick">
+        <input type="hidden" name="hosted_button_id" value="BPCLP83DFF2N2">
+    </form>
+    <img onclick="$('#paypal_donate').submit();"
+        src="http://celeryproject.org/static/img/icon-paypal.png" alt="amex">
+    <iframe style="border: 0; margin: 0; padding: 0;"
+            src="https://www.gittip.com/ask/widget.html"
+            width="48pt" height="22pt"> </iframe>
+</div>

docs/.templates/sidebarlogo.html

@@ -1,3 +1,15 @@
 <p class="logo"><a href="{{ pathto(master_doc) }}">
   <img class="logo" src="http://cloud.github.com/downloads/celery/celery/celery_128.png" alt="Logo"/>
 </a></p>
+<div id="donate">
+    <b>Please donate:</b>
+    <form id="paypal_donate" action="https://www.paypal.com/cgi-bin/webscr" method="post">
+        <input type="hidden" name="cmd" value="_s-xclick">
+        <input type="hidden" name="hosted_button_id" value="BPCLP83DFF2N2">
+    </form>
+    <img onclick="$('#paypal_donate').submit();"
+        src="http://celeryproject.org/static/img/icon-paypal.png" alt="amex">
+    <iframe style="border: 0; margin: 0; padding: 0;"
+            src="https://www.gittip.com/ask/widget.html"
+            width="48pt" height="22pt"> </iframe>
+</div>