Update install instructions
Update install instructions

mysociety/popit,Sinar/popit,Sinar/popit,mysociety/popit,openstate/popit,mysociety/popit,openstate/popit,openstate/popit,mysociety/popit,mysociety/popit,Sinar/popit,maxogden/popit,maxogden/popit,openstate/popit,Sinar/popit