If you keep your config in the data directory, in the default PostgreSQL style, probably the simplest way to do this is to create a git repository with a symbolic link to the data directory and a .gitignore that ignores everything in the data directory but the config files. The add the config files and you're done. If you keep the config files separately, as Debian does, then you can probably just create a git repository right in the config directory if you don't already have one at a higher level.
I have been guilty of not doing this in the past, but I have come to the strong conclusion that this should be a part of standard best practice.
My attention has been drawn to etckeeper, which makes handling this super simple when you're using Debian-style config setups. It's available both for Debian and for RedHat-ish systems, as well as possibly others.