Add DissidentX to Resources

This is more of a proposal since [DisidentX](https://github.com/bramcohen/DissidentX) does not provide any methods for message distribution per se though it could be a basis of such system. Bram even [offers some ideas](https://github.com/bramcohen/DissidentX#primary-use) on how it could work:

> The primary use case for DissidentX is encoding messages in files on the web.
>
> There should be a utility which scans all objects the user's web browser downloads (html files, images, css files, etc.) for messages using all of the keys the user has entered. Someone sending messages to that person provides a web service where users who have widely viewed web sites can upload their files and get back slightly modified version with messages steganographically added.
>
> The web users should not be able to read what the messages are, and it should be possible for the service doing the encoding to not have to keep messages in plaintext.

What do you think?