Add docs and a user friendly README

[svenstaro]

Currently as a user coming into this project, I have 0 idea what embuild is meant to do for me as a whole. Could you add an overall README?

[ivmarkov]

Sure. When I get to it. PRs greatly appreciated though!

[svenstaro]

But I don't actually know the scope nor goal hence this issue. :D

[ivmarkov]

Then this will stay open until I or someone else will fi d the time to invest into it. The point is, we really also need the help of the community in some of these things. Perhaps this particular issue is not the best example (docu of unknown code etc.) but there are a lot of other places where folks can help.

[N3xed]

Fixed by 653f703 and 14c2bb6.
There is always room for improvement, but this should suffice for now.