Re-add CHANGELOG file.
Re-add CHANGELOG file.

Various important (structural) changes are being made and expecting
everyone to check `git log` to find out about them, is not reasonable.

Signed-off-by: Diederik de Haas <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@cknow.org>

yodaaut/raspbian-ua-netinst