In the System Settings documentation we recommend exporting a configuration file rather than crafting one by hand. This way our end users don't need to dig into the source code for arcane PIDs and method names to find out the name of their file and how to refer to the config options.
It's important to have this in Instance Settings as well.
System Settings provides an Export option that becomes available once you modify a configuration entry. Exporting is the best way to create .config files: you download a .config file containing the entry's settings in a key=value format, then modify or distribute as you have need. All available configuration keys and values are exported, even if only one value was changed.