Update de.json

Added instructions how to use GnuGP under Windows, Ubuntu and OS X.
You might want to check out:

https://play.google.com/store/apps/details?id=org.thialfihar.android.apg

"OpenPGP for Android. It's open source and its goal is to provide a similar OpenPGP implementation as GnuPG.

NOTE: Internet permissions are ONLY used for key server queries. I didn't like the idea of APG requesting those permissions either, but it is open source and the code shows that it doesn't use those permissions for anything else."