Put in full defcomponent example that compiles on vanilla Clojure/Om

Hi, feel free to ignore this if I missed something, but that ":- {:init number}" part on defcomponent doesn't seem to compile on vanilla Clojure/Om, not sure what that's about. Also, since all you need is 3 more lines of code to turn the snippet into a fully formed Om app, it would help to just put that in for people trying to grok your library.