[contributor] Explains how to build PDF files
[contributor] Explains how to build PDF files

PDF builds in openstack-manuals are now supported with --pdf option.
It is a good idea to mention how to build PDF files with
library dependencies.

Change-Id: I40902bb09ee18fda67d6f6cafaf2caf2f05f5c59
Implements: blueprint build-pdf-from-rst-guides

openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals