Added a guide to have multiple application in a single app.

We had multiple tool applications and we wanted to group them in a portal.
A saw a post on SO of someone who wanted to do something similar but without any answers and I had time for R&D so I used it to find a solution.
(http://stackoverflow.com/questions/18461997/how-to-run-multiple-applications-under-one-compoundjs-instance)

I analysed the workflow of Compound and found a way to include child applications as node_module in a parent's Compound application without doing any change in compound source code.

We have 4 applications working together without any problems so far (the portal and 3 tools).
Two of the tools are using AngularJS without problem (which is why there is an Angular section in the guide).
Each of the child application can still be run in standalone for easier development.

I had the guide tested by one of my co-worker for one of the tool and he could make it work, so I think it's easy enough to read.

I have been suggested by another co-worker to share my solution to help others and maybe get feedback, so here it is !
I hope you like it enough to merge it.

PS. The link in README.md already directs toward the future location on your server, so it's 404 for now.