updated readme to reflect the fact that eigen is now optional
updated readme to reflect the fact that eigen is now optional

wgmueller1/pyhsmm,wgmueller1/pyhsmm,wgmueller1/pyhsmm,theDataGeek/pyhsmm,mattjj/pyhsmm,bikash/pyhsmm,theDataGeek/pyhsmm,bikash/pyhsmm,theDataGeek/pyhsmm,fivejjs/pyhsmm,bikash/pyhsmm,theDataGeek/pyhsmm,wgmueller1/pyhsmm,fivejjs/pyhsmm,fivejjs/pyhsmm,fivejjs/pyhsmm,mattjj/pyhsmm,wgmueller1/pyhsmm,theDataGeek/pyhsmm,fivejjs/pyhsmm