applets/systemtray: warn people about disabling klipper
Reason for the change
When you do this, you lose all clipboard history, including keeping copied stuff when the app it came from closes. This is non-obvious, and I've seen a number of confused people complaining about it over the years.
Add a warning about this so people will at least have the opportunity to learn that what they're doing is not recommended.
Test plan
- Show System Tray config window > Entries page
- set "Clipboard" to "Disabled"
Screenshots or screen recordings
Edited by Nate Graham