Misc README tweaks
Misc README tweaks

* Rewrote the introduction a bit

* Rewrote the "Support/Contributing" section

* Rewrote the "Writing a notifier" section

* Removed 'require "rubygems"' from examples

* Misc tweaks. Remove unused links, puts them under
  relevant para.

* "Point demo to ci.atonie.org for now as I can't get `thin`
  to work on r2d2 (the server that used to host the demo)

integrity/integrity,faradayio/ci1,factorylabs/integrity,integrity/integrity,p/integrity,forresty/integrity,p/integrity,forresty/integrity,factorylabs/integrity,erik-escobedo/integrity,faradayio/ci1,dkastner/prism_ci,erik-escobedo/integrity,integrity/integrity