Bug#806904: documenting how to switch to gpg 2.1 is done

[Daniel Kahn Gillmor]

users can now switch to gpg version 2.1.x by doing "apt upgrade" :)

after the upgrade, users can also read
/usr/share/doc/gnupg/README.Debian if they want more detail.

So i think it's fine to close 806904 now.

   --dkg