Update the image-building documentation
Update the image-building documentation

Small sphinx syntax fixes, better wording, removed pronouns, and
anything else we can think of.

Change-Id: Id7ca8d4673f987d10b520cb1eab77802a043c223
Partially-implements: blueprint documentation-rework

rahulunair/kolla,GalenMa/kolla,mandre/kolla,dardelean/kolla-ansible,stackforge/kolla,mandre/kolla,mrangana/kolla,coolsvap/kolla,openstack/kolla,dardelean/kolla-ansible,stackforge/kolla,intel-onp/kolla,openstack/kolla,nihilifer/kolla,coolsvap/kolla,stackforge/kolla,tonyli71/kolla,tonyli71/kolla,coolsvap/kolla,mandre/kolla,mrangana/kolla,GalenMa/kolla,intel-onp/kolla,rahulunair/kolla,nihilifer/kolla,dardelean/kolla-ansible