add Overlay for **app** (if it exists) and add it to the config file; [app] is the name of the app's directory in `/system/app` or `/system/priv-app`
`-r`, `--remove` [app]
remove Overlay for **app** (if it exists) and remove it from the config file; [app] is the name of the app's directory in `/system/app` or `/system/priv-app`
`-s`, `--show`
show all apps that **don't** have an Overlay (slow)
`-l`, `--list`
show all apps that **do** have an Overlay
`-x`, `--create`
create Overlays from config file
`-u`, `--update`
remove existing Overlays and re-create them from the config file