Hide the defunct FPS checkbox in settings menu, added hint text for f3 binding

files/mygui/openmw_settings_window.layout

@@ -256,6 +256,8 @@
                             </Widget>
                         </Widget>
                         <Widget type="HBox" skin="" position="182 94 300 24">
+                            <Property key="Visible" value="false"/>
+                            <UserString key="Hidden" value="true"/>
                             <Widget type="AutoSizedButton" skin="MW_Button" position="0 0 24 24" align="Left Top" name="FPSButton"/>
                             <Widget type="AutoSizedTextBox" skin="SandText" position="28 4 32 16" align="Left Top">
                                 <Property key="Caption" value="FPS"/>
@@ -273,6 +275,12 @@
                                 <Property key="Caption" value="Object shaders"/>
                             </Widget>
                         </Widget>
+
+                        <Widget type="TextBox" skin="SandText" position="182 94 300 32" align="Left Top">
+                            <Property key="MultiLine" value="true"/>
+                            <Property key="Caption" value="Hint: press F3 to show \nthe current frame rate."/>
+                        </Widget>
+
                         <Widget type="TextBox" skin="NormalText" position="0 198 329 18" align="Left Top" name="FovText">
                             <Property key="Caption" value="Field of View"/>
                         </Widget>