Added some more metadata to introduction

docs/includes/introduction.txt

@@ -1,6 +1,9 @@
 .. image:: http://cloud.github.com/downloads/ask/celery/celery_favicon_128.png
 
 :Version: 1.0.0
+:Web: http://celeryproject.org/
+:Download: http://pypi.python.org/pypi/celery/
+:Source: http://github.com/ask/celery/
 :Keywords: task queue, job queue, asynchronous, rabbitmq, amqp, redis,
   django, python, webhooks, queue, distributed