Inform user that OpenGL render needs restart

src/ui/settings_app.ui

@@ -174,7 +174,7 @@
         <number>0</number>
        </property>
        <property name="currentIndex">
-        <number>1</number>
+        <number>0</number>
        </property>
        <widget class="QWidget" name="page_main">
         <layout class="QVBoxLayout" name="verticalLayout_5">
@@ -521,7 +521,7 @@
             <item>
              <widget class="QCheckBox" name="cb_canvas_use_opengl">
               <property name="text">
-               <string>Use OpenGL for rendering (EXPERIMENTAL)</string>
+               <string>Use OpenGL for rendering (EXPERIMENTAL, needs restart)</string>
               </property>
              </widget>
             </item>