readme: add note on pip installation
readme: add note on pip installation

willu47/smif,willu47/smif,tomalrussell/smif,tomalrussell/smif,tomalrussell/smif,tomalrussell/smif,nismod/smif,willu47/smif,nismod/smif,nismod/smif,nismod/smif,willu47/smif