OpenBCI_Python cannot find "streamer lsl" as plugin

Just i've a problem with python. I think i download everything but when i put  the sentence

python user.py –board cyton -p *cyton address* -a streamer_lsl

Terminal
tells me that he could not find "streamer lsl" as plugin . You know
why?  I'v download too the folder  "labstreaminglayer-master" for python

thank you