mention on path attacks in 7.1

[klarose]

When we trust a network, we introduce the risk of on path attacks. Mention a few of them as possibilities.

Fixes #110

A few questions for the reviewers:

• Should we mention that the list is not exhaustive, or is that implied?
• Should we mention mitigating factors? (i.e. some of the attacks I've mentioned should be prevented w/ proper use of TLS).