README.md: put correct name of futures package
README.md: put correct name of futures package

shlomif/rhizi,tlevine/rhizi,cben/rhizi,tlevine/rhizi,yuvadm/rhizi,tlevine/rhizi,tlevine/rhizi,yuvadm/rhizi,Rhizi/rhizi,Rhizi/rhizi,yuvadm/rhizi,shlomif/rhizi,cben/rhizi,yuvadm/rhizi,ozFri/rhizi,shlomif/rhizi,shlomif/rhizi,ozFri/rhizi,ozFri/rhizi,cben/rhizi,cben/rhizi,Rhizi/rhizi,Rhizi/rhizi,ozFri/rhizi