autohelp: remove out of date doc in README.md
autohelp: remove out of date doc in README.md

Provide a link to the openstack-doc-tools readme.

Change-Id: I05b3b08ac97c9820896ef3318fbf60522fd41b5e

gongysh2004/openstack-manual,openstack/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,kairoaraujo/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,potsmaster/openstack-manuals,saeki-masaki/openstack-manuals,openstack/openstack-manuals,saeki-masaki/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals,kairoaraujo/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,Akasurde/openstack-manuals,gongysh2004/openstack-manual,potsmaster/openstack-manuals,Akasurde/openstack-manuals