data/ui/application.ui: Add menu entry for keyboard shortcut dialog

Author: kaiw

data/ui/application.ui

@@ -57,6 +57,10 @@ Josef Vybíral</property>
         <attribute name="action">app.help</attribute>
         <attribute name="accel">F1</attribute>
       </item>
+      <item>
+        <attribute name="label" translatable="yes">Keyboard Shortcuts</attribute>
+        <attribute name="action">win.show-help-overlay</attribute>
+      </item>
       <item>
         <attribute name="label" translatable="yes">_About</attribute>
         <attribute name="action">app.about</attribute>