docs: chore: recommend files module instead of COPY

README.md

@@ -29,7 +29,7 @@ After setup, it is recommended you update this README to describe your custom im
 
 The easiest way to start customizing is by looking at and modifying `config/recipe.yml`. It's documented using comments and should be pretty easy to understand.
 
-If you want to add custom configuration files, you can just add them in the `/usr/etc/` directory, which is the official OSTree "configuration template" directory and will be applied to `/etc/` on boot. `config/files/usr` is copied into your image's `/usr` by default. If you need to add other directories in the root of your image, that can be done in the Containerfile. Writing to `/var/` in the image builds of OSTree-based distros isn't supported and will not work, as that is a local user-managed directory!
+If you want to add custom configuration files, you can just add them in the `/usr/etc/` directory, which is the official OSTree "configuration template" directory and will be applied to `/etc/` on boot. `config/files/usr` is copied into your image's `/usr` by default. If you need to add other directories in the root of your image, that can be done using the `files` module. Writing to `/var/` in the image builds of OSTree-based distros isn't supported and will not work, as that is a local user-managed directory!
 
 For more information about customization, see [the README in the config directory](config/README.md)
 
@@ -95,4 +95,4 @@ Then type `just` to list the just recipes available.
 
 The file `/usr/share/ublue-os/just/custom.just` is intended for the custom just commands (recipes) you wish to include in your image. By default, it includes the justfiles from [`ublue-os/bling`](https://github.com/ublue-os/bling), if you wish to disable that, you need to just remove the line that includes bling.just.
 
-See [the just-page in the Universal Blue documentation](https://universal-blue.org/guide/just/) for more information.
+See [the just-page in the Universal Blue documentation](https://universal-blue.org/guide/just/) for more information.