Mention QDialog::setSizeGripEnabled() in QSizeGrip's docs

The same way it also mentions QStatusBar.

Change-Id: Ic084466310c989d1a79ba5ba21d6784acaa38e6e
Reviewed-by: Martin Smith <martin.smith@theqtcompany.com>

src/widgets/widgets/qsizegrip.cpp

@@ -178,9 +178,12 @@ Qt::Corner QSizeGripPrivate::corner() const
     Put this widget anywhere in a widget tree and the user can use it
     to resize the top-level window or any widget with the Qt::SubWindow
     flag set. Generally, this should be in the lower right-hand corner.
+
     Note that QStatusBar already uses this widget, so if you have a
     status bar (e.g., you are using QMainWindow), then you don't need
-    to use this widget explicitly.
+    to use this widget explicitly. The same goes for QDialog, for which
+    you can just call \l {QDialog::setSizeGripEnabled()}
+    {QDialog::setSizeGripEnabled()}.
 
     On some platforms the size grip automatically hides itself when the
     window is shown full screen or maximised.