Documentation clarification requests

[adw96]

I spoke to a first time radEmu user yesterday -- an experienced coder who just wanted the basic overview more quickly. Let's make it easier for those folx to find what they need.

Specifically,

1. make what appears with ?emuFit clearer. In particular, talk a first timer through the most important output. Emphasise that estimates are on log-fold difference scale, give eg here on how to describe on FD scale. perhaps give example interpretation.
2. "TL;DR vignette". Just show how to run emuFit and interpret output. One example that is independent data, another that is cluster correlated (since many people have this)

[svteichman]

These are addressed in PR #180!