This let me to the question of how can I easily add a new configuration file? I figured that some files must just be picked up automatically but was it really just as simple as adding another line to something like my local.conf? The simple answer is YES.
You can just add a line like:
The only thing to be aware of is that you can either "include" a configuration file, which means that it will be used if it exists but if it doesn't exist that's OK. Or you can "require" a configuration file, which as the name implies means it has to be present or you will get an error.
As for adding a configuration file "automatically" I'm not sure how to do that and I have it on good advice that you don't want to do that. I guess I can understand that because it is nice to know explicitly how something got added and forget all the automagical stuff.