Update section about Tor

[runasand]

This section should ideally focus on helping the user understand how Tor works, how to use it, and how to use it correctly. A small section on Tor for mobile users would probably benefit users. Updated images and screenshots would be helpful. Pitfalls such as unencrypted sites, Flash, additional extensions, and PDF documents should be explained as well. We know the NSA tried (and failed) to break Tor, that probably deserves a mention.