Documentation suggestion

[OrangeDog]

Can't find the source to make a PR so...

When creating a role for zabbiz-agent to use, the simplest way to achieve the correct permissions is to make it a member of the default pg_monitor role.

CREATE ROLE zabbix WITH LOGIN IN ROLE pg_monitor;

Uisng the name zabbix also means that peer authentication can be used in a default installation, without having to configure pg_ident.conf.

[cavaliercoder]

Very cool! pg_monitor did not exist prior to PostgreSQL 10. Definitely would like to include this in the docs.

It's been a while since I compiled the docs, but I recall their being advice against using peer auth at the time. I'll look into this again.

If you'd like to submit a PR, documentation is in the gh-pages branch of this repo.