Correct docs link address in README
Correct docs link address in README

Change-Id: I23c9d3b3111b6c0a468ed6c467416465429a39ef

NeCTAR-RC/horizon,yeming233/horizon,BiznetGIO/horizon,ChameleonCloud/horizon,yeming233/horizon,ChameleonCloud/horizon,ChameleonCloud/horizon,BiznetGIO/horizon,noironetworks/horizon,yeming233/horizon,NeCTAR-RC/horizon,openstack/horizon,noironetworks/horizon,openstack/horizon,yeming233/horizon,BiznetGIO/horizon,NeCTAR-RC/horizon,ChameleonCloud/horizon,NeCTAR-RC/horizon,noironetworks/horizon,openstack/horizon,openstack/horizon,BiznetGIO/horizon,noironetworks/horizon