Restore InkHUD to defaults on factory reset (#6637)

* Erase InkHUD settings on factory reset

* Documentation

* Captialn't
Lower case m. Also move the include statement to .cpp, because it doesn't really need to be in the .h

src/graphics/niche/InkHUD/docs/README.md

@@ -502,6 +502,10 @@ Applets themselves do also listen separately for various events, but for the pur
 
 Button input is sometimes handled by a system applet. `InkHUD::Events` determines whether the button should be handled by a specific system applet, or should instead trigger a default behavior
 
+#### Factory Reset
+
+The Events class handles the admin messages(s) which trigger factory reset. We set `Events::eraseOnReboot = true`, which causes `Events::onReboot` to erase the contents of InkHUD's data directory. We do this because some applets (e.g. ThreadedMessageApplet) save their own data to flash, so if we erased earlier, that data would get re-written during reboot.
+
 ---
 
 ### `InkHUD::Applet`