Document possibility to use imaxima

FYI, I was just (again) trying out this package and also imaxima. Imaxima offers the (default) option to print output as printed latex equations. It can easily be used as inferior process buffer by setting the variable imaxima-use-maxima-mode-flag to t and then starting imaxima before creating an inferior process with maxima.el

The latex output size can be customized with the imaxima-fnt-size and imaxima-pt-size variables.

I did not read anything about this in the README, so I just wanted to inform you about it