Merge pull request #3 from str4d/anon-usage-documentation

Changes required for safe txi2p use
Change dialectic from Tor to anonymizing network

Here we include skeleton sections for I2P... as well as
changing our description to talking about I2P and Tor as
possible anonymizing networks to use with Tahoe.
Removed I2P ticket info because it belongs in a trac ticket
Fix formatting
I2P information