readme: add contact section
readme: move packaging section into real documentation

I would like to keep the README short and to the point. So reference
information like how to create a package is better placed in the
larger documentation.
packaging: consistent markup for filenames
packaging: fix capitalization
packaging: there is no need to specify Git clone directory

We don't refer to $HOME again, so just let the readers decide this by
themselves.
packaging: focus on preferred way to update changelog
readme: add small intro text
Merge pull request #145 from mgeisler/readme-updates

Readme updates