Update README to properly explain usage of package.json targets

[andytudhope]

After cleaning up our dependencies and finding clarity on how we are integrating Embark (both contract objects and embark-js), we need to adjust the Makefile to build our new FE properly, zip it all up and make it pretty enough to simply drop into Amazon EB as we currently do.

This will require input from @jakubgs when we are ready with some of the other steps.

[jakubgs]

After talking with Richard the most sensible thing to do would be probably to ditch the Makefile and re-doing the whole build process from scratch in something like Gulp/Grunt/Whatever. But to do that we'd have to essentially split the build process into it's distinct parts and make sure they work individually. Only then can we reliably combine them into a single pipeline.

[andytudhope]

We may still end up using the Makefile, but we need to update the README to explain clearly how to use which targets in package.json (including which version of node to use etc.)