Add links to the great screen casts on git-flow to the README.

Thanks Mark and David!
diff --git a/README.mdown b/README.mdown
index 1147423..e4f3682 100644
--- a/README.mdown
+++ b/README.mdown
@@ -134,6 +134,11 @@
 
 [http://jeffkreeftmeijer.com/2010/why-arent-you-using-git-flow/](http://jeffkreeftmeijer.com/2010/why-arent-you-using-git-flow/)
 
+Or have a look at one of these screen casts:
+
+* [A short introduction to git-flow](http://vimeo.com/16018419) (by Mark Derricutt)
+* [On the path with git-flow](http://codesherpas.com/screencasts/on_the_path_gitflow.mov) (by Dave Bock)
+
 
 ### Initialization