Make easier on new devs

I added some extra information to README.development to make it completely obvious in case anybody runs into some problems. 

The README.development was already pretty clear, but I managed to overlook the obvious and managed to waste 2 hours, so in case it happens to anybody else, I made this change.

I expect you may have concerns with it being too Debian specific? In which case I'm happy to research what  you'd do on a RH based systems, also BSD with ports and Mac with ports/brew.

Also, if you want to reject this on the basis that it might make already reasonably clear instructions less concise and verbose, I understand. I just did it in case someone else bumped into this, and to save others time.