Install Guide: Edit on ch_basics

As suggested by Diane in
https://review.openstack.org/#/c/55954/1/doc/install-guide/

Change-Id: Ide8aa9d8d1c81c331929f658b1148b2d88a316f6
backport: havana
(cherry picked from commit 59da2263744fd1efbdfbe61e8588db3c741d11c4)