added BugStage update command

plugins/ghupdate/ghupdate.go

@@ -1,6 +1,9 @@
 // Package ghupdate implements a new command to selfupdate the current
 // PocketBase executable with the latest GitHub release.
 //
+// This is kept only for backward-compatibility and it is replaced by
+// the equivalent `update` BugStage plugin.
+//
 // Example usage:
 //
 //	ghupdate.MustRegister(app, app.RootCmd, ghupdate.Config{})