Update index.rst
Update index.rst

Minor typo where there was two "pip install" in the dev version installation command line. 

From this: 
    pip install pip install git+https://github.com/scrapy/slybot.git

To this:
    pip install git+https://github.com/scrapy/slybot.git
sntran/portia,livepy/portia,NicoloPernigo/portia,lodow/portia-proxy,hanicker/portia,asa1253/portia,chennqqi/portia,Suninus/portia,sntran/portia,verylasttry/portia,verylasttry/portia,livepy/portia,flip111/portia,hanicker/portia,SouthStar/portia,anjuncc/portia,CENDARI/portia,pombredanne/portia,naveenvprakash/portia,Youwotma/portia,hmilywb/portia,sntran/portia,chennqqi/portia,naveenvprakash/portia,verylasttry/portia,amikey/portia,Youwotma/portia,nju520/portia,CENDARI/portia,NoisyText/portia,naveenvprakash/portia,amikey/portia,PrasannaVenkadesh/portia,hmilywb/portia,NoisyText/portia,NoisyText/portia,chennqqi/portia,flip111/portia,lodow/portia-proxy,hmilywb/portia,anjuncc/portia,PrasannaVenkadesh/portia,flip111/portia,CENDARI/portia,CENDARI/portia,NoisyText/portia,hanicker/portia,Youwotma/portia,Suninus/portia,pombredanne/portia,amikey/portia,livepy/portia,NicoloPernigo/portia,anjuncc/portia,nju520/portia,livepy/portia,naveenvprakash/portia,Youwotma/portia,lodow/portia-proxy,nju520/portia,asa1253/portia,sntran/portia,anjuncc/portia,Suninus/portia,NicoloPernigo/portia,asa1253/portia,hmilywb/portia,asa1253/portia,pombredanne/portia,amikey/portia,pombredanne/portia,Suninus/portia,flip111/portia,NicoloPernigo/portia,hanicker/portia,SouthStar/portia,SouthStar/portia,nju520/portia,PrasannaVenkadesh/portia,chennqqi/portia,PrasannaVenkadesh/portia,SouthStar/portia,verylasttry/portia