Updated readme file for pip installation method.
Updated readme file for pip installation method.

johnmcdonnell/psiTurk,andyh616/psiTurk,pfeyz/psiTurk,berkeley-cocosci/psiTurk,pfeyz/psiTurk,suchow/psiTurk,michaelpacer/psiTurk,johnmcdonnell/psiTurk,suchow/psiTurk,andyh616/psiTurk,michaelpacer/psiTurk,mshvartsman/psiTurk,berkeley-cocosci/psiTurk,johnmcdonnell/psiTurk,kachergis/psiTurk,rbtrace/psiTurk,NYUCCL/psiTurk,michaelpacer/psiTurk,mshvartsman/psiTurk,andyh616/psiTurk,mshvartsman/psiTurk,rbtrace/psiTurk,NYUCCL/psiTurk,berkeley-cocosci/psiTurk,kachergis/psiTurk,rbtrace/psiTurk,kachergis/psiTurk,suchow/psiTurk,pfeyz/psiTurk,NYUCCL/psiTurk