[doc/book] Improve installation doc mostly about pip ans easy_install
the documentation now informs about compatibility and recommendation for pip and
easy_install.
#! /bin/sh -ecase "$1" in remove) if [ -x "/etc/init.d/cubicweb-ctl" ]; then invoke-rc.d cubicweb-ctl stop || true fi ;;esac#DEBHELPER#exit 0