Missing wiki page for build.sh

A wiki page explaining the options and behavior of build.sh would be useful for new users.

As it's done now, my idea is that real beginners can run RouteFlow at first following the simple instructions in the README. For any other use (Ryu, HA, newer OVS versions...) they'd use the build script.

All code in the core RouteFlow distribution should be compatible with both the simple steps (and the dependencies they pull) and the dependencies installed using build.sh.

[joestringer]

Build.sh has a -h option, that seems the best way for new users to find out how it works. Otherwise, updates to the repository would need to be mirrored to the wiki every time.