Add Docs (or Reference) For Standard Shell Commands (e.g. script)

http://stackoverflow.com/questions/24819401/how-to-get-spring-xd-to-deploy-a-predefined-set-of-streams-and-taps-on-startup

It is documented here https://github.com/spring-projects/spring-xd/wiki/Shell#executing-a-script

But maybe it should also be at the top of the appendix?

https://github.com/spring-projects/spring-xd/wiki/ShellReference