Have better explanation for Q-squared values

[mortonjt]

We will want to have a more explicit definition of this at some point

The formula was inspired by the pseudo R2 http://www3.stat.sinica.edu.tw/statistica/oldpdf/a16n39.pdf

It'll be great to have the pseudo R2 working - will need a dataset to better showcase this (it looks like the red sea dataset doesn't have enough data points for this)