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."
Update de.json

minor fix
Merge pull request #314 from MenMan/patch-13

Patch 13