docs(apps): clarify ping URL only accepts http/https

apps/docs/docs/management/apps/index.mdx

@@ -47,6 +47,7 @@ You can also use custom URI schemes such as `vscode://file/path`, `microsoft-edg
 When you want to use another url for the simple status check you can set it here.
 This will allow you to set a different URL for the ping than the URL that is opened when clicking on the app widget.
 It's useful when you want to ping the service internally for example with a custom ip but open the website externally.
+Note that the ping URL only accepts `http://` and `https://` URLs — custom URI schemes are not supported for pings.
 
 ## List of apps