Added online demo to the README

README.md

@@ -24,9 +24,10 @@ Key features include:
 See the [documentation](https://pyddm.readthedocs.io/en/latest/index.html),
 [FAQs](https://pyddm.readthedocs.io/en/latest/faqs.html), or
 [tutorial](https://pyddm.readthedocs.io/en/latest/quickstart.html) for more
-information.  See the [Github
-Forums](https://github.com/mwshinn/PyDDM/discussions) for help from the PyDDM
-community.  You can also sign up for [release announcements by
+information.  You can also try the [Interactive online
+demo](https://colab.research.google.com/github/mwshinn/PyDDM/blob/master/doc/notebooks/pyddm_demo_leaky_collapse.ipynb>).
+See the [Github Forums](https://github.com/mwshinn/PyDDM/discussions) for help
+from the PyDDM community.  You can also sign up for [release announcements by
 email](https://www.freelists.org/list/pyddm-announce).