Include secure messaging in /guide/internet-security.md

[robotfactory]

The normal person's guide to internet security is great, but I think it should mention ways to keep messaging like SMS, IMs, or emails more secure. Even a short list of recommended services could be very helpful.

If you want to expand the list beyond six things I can fork and submit some PRs if you'd like.

[mkiser]

Sure, go for it. Just keep it in the realm of "normal people" – this stuff easily becomes too advanced for the average user.