update README

Made 3 distinct steps, clarified packaging, moved running bot at end (not needed by most people), ensured correct capitations.

Diff is confusing; easier just to [read directly](https://github.com/tomByrer/libgrabber/blob/master/README.md)
Thanks; these 3 lines are my main reason for re-writing the README.  My impression was there were 8 steps to get libgrabber to work, but there really are only 3.