More comments, + patch for Jeff

Added more comments to the analyzeZData.Rmd file, confirmed that it
runs on my computer. Has a problem where it reports not having done
mixture models for GATA2A and GATA5, despite having done so. Added a
brief “patch” that forces it to do them again after the other genes,
which seems to work. Also added code that exports the zfi and zfim
object so don’t have to keep re-running this code over and over.