docs: move some of them to the root directory

Lets move CodingStyle, SubmittingPatches, and Sponsors into the
root directory of netsniff-ng and remove the Documentation folder.
Some of those files are quite bloated, and most of these things
should be in the man-pages anyway. They should be the only big
sources of documentation, nothing else.

The rest is currently put here: http://pub.netsniff-ng.org/docs/

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
docs: readme: add steps to verify a Git release

We should only put the things here that are interesting for users,
thus, add steps to verify a release from the Workflow document.

 [1] http://pub.netsniff-ng.org/docs/Workflow

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
build: currently do not copy docs to shared docs

Maybe in short term future, before the next release, we will think
about putting the README file for users into DOCDIRE, since the
rest is not really interesting for users, but probably only for
developers.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>