Update section on Readability, Gunning Fog index, etc.

[daobrien]

https://bugzilla.redhat.com/show_bug.cgi?id=1019258 https://mojo.redhat.com/people/lnovich/blog/2014/07/01/flesh-kinkaid-readability-and-your-documents-this-is-the-number-that-matters

A range of info from Laura that needs to be incorporated.