Mailvelope setup on Linux Mint

Unlike the easy installation process on Windows platform, on linux to make Mailvelope use GnuPG you have to follow the official instructions.

https://github.com/mailvelope/mailvelope/wiki/Mailvelope-GnuPG-integration

You need to first install the package gpgme of course, but what is missing on the official instruction is that you also have to install gpgme-json, which seems to be not included in gpgme.

sudo apt-get install libgpgme-dev

sudo apt-get -y install gpgme-json

After that check if the file /usr/bin/gpgme-json exists. Then follow the instruction for creating the manifest file: https://github.com/mailvelope/mailvelope/wiki/Creating-the-app-manifest-file-on-macOS-and-Linux 

Restart the browser, you can now see the OpenGPG is available now.