Add mention of firewall ports to installation guide and in FAQ

Currently we reference ports in the glossary, but it is not mentioned in the installation guide nor in the FAQ. I think we should list in both places.  Specifically in the installation guide, we should advise users that they need to open any firewall ports when adding services.

Add to this section of install guide: https://www.percona.com/doc/percona-monitoring-and-management/deploy/index.html#collecting-data-from-pmm-abbrev-clients-on-pmm-abbrev-server

Add to FAQ: https://www.percona.com/doc/percona-monitoring-and-management/faq.html

Content is here (ports section): https://www.percona.com/doc/percona-monitoring-and-management/glossary.terminology.html