Create guide on adjusting parameters on new data (and FAQ)

[jmbhughes]

It would be good to create a guide for new users on how to adjust parameters (psf window size, target psf parameters, alpha, epsilon, etc.) to deal with commonly seen problems (boxes around stars, Fourier ringing, black circles around stars) when using the technique on a new dataset. This stems from discussion in #47. @sumanchapai may have insight that they learn from this procedure on their data. @svank also might have ideas from his work.