Create instructions for maven assembly for acmeair loader

The instruction at https://github.com/acmeair/acmeair/wiki/WebSphere-Liberty-To-WebSphere-eXtreme-Scale-Setup launch Acmeair Loader via mvn:exec 

I am preparing a lab in which Acmeair Loader is run and compiled upon two different boxes; therefore I have added instructions for maven assembly to create an acmeair-loader jar which I can transfer across to the second box.