man: mausezahn: add howto for interactive mode

It is quite useful to have an initial walkthrough for the interactive
mode documented, so add a first version of this [1] into the man page.

  [1] original here: http://pub.netsniff-ng.org/docs/Mausezahn

Formatting still needs to be fixed up in follow-up commits.

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