Clarify unrelated to pycon.org

As written, the readme implies that this repository feeds into
www.pycon.org. This change clarifies the fact that the repo here is
standalone. For related issues regarding displaying this data, see #89
and #153.

README.md

@@ -1,7 +1,8 @@
 # Python Conferences
 
-Here is a list of [Python Conferences](http://www.pycon.org) around
-the World.
+Here is a list of Python Conferences around the world. Note: this repository
+does not power www.pycon.org; to add an event to www.pycon.org, see [its
+official repository](https://github.com/PyCon/pycon.org#adding-your-pycon-to-the-website).
 
 If you would like to add a conference, please [submit a pull
 request](https://github.com/python-organizers/conferences/pulls).