beginnings of elementary usage

A shell of a document and request for its completion.

I've had/having difficulty exploring the full functionality of git-deploy. The merging and completion of a primer would be helpful to me and possibly other users.

There's also a [demo](https://github.com/kiwiroy/git-deploy-demo) repository, that you should feel free to fork, take ownership of or otherwise contribute to.

Looking forward to comments.