clearify need to websocket-client

[parviz-binary]

add this line to the top of the python demo:

install "websocket-client" (instead of "websocket") for using "websocket" package

[ghost]

Hi, sorry about the reference, I was experimenting with a bash script and accidentally push unrelated code to my fork of websockets and unfortunately those commits has references (#132 in particular) from a different project and GitHub picked up on it.