Remove ChangeLog, add README.coding

Removed the ChangeLog, from now on we go with the git commit messages. One source
less for merge conflicts.

Also added a README.coding, mostly a copy from dakV2. I very much love to get code
from others, so to not annoy new committers too much, lets go and write the basic
rules I try to apply down here. Better than nagging after I got a patch to merge.

Signed-off-by: Joerg Jaspert <joerg@debian.org>