Add help url placeholders for new pages

Bug: 38412798
Test: visual
Change-Id: I4ede523cb13790ea05309279f80a778b2086f850

src/com/android/settings/system/SystemDashboardFragment.java

@@ -54,6 +54,11 @@ public class SystemDashboardFragment extends DashboardFragment {
         return R.xml.system_dashboard_fragment;
     }
 
+    @Override
+    protected int getHelpResource() {
+        return R.string.help_url_system_dashboard;
+    }
+
     @Override
     protected List<PreferenceController> getPreferenceControllers(Context context) {
         return buildPreferenceControllers(context);