System updates app does not inform me if I have switched device to "developer mode"

[Stuart Langridge]

If I have put my Ubuntu Touch device in "developer mode", that is made it read-write so I can install arbitrary packages and edit system files by touching/userdata/.writable_image (as per https://wiki.ubuntu.com/Touch/Install#Step_4_-_Downloading_.26_Deploying_Image_to_Device) then the System Updates app will no longer install system updates. However, the System Updates app does not *say* this: it still looks like it should work as normal. If the device is in rw "developer" mode, the System Updates app could say something like "Device is in developer mode; to apply system updates, switch back out of developer mode" or similar.