Add some missing docs

git-svn-id: svn+ssh://svn.code.sf.net/p/supertuxkart/code/main/trunk@8557 178a84e3-b1eb-0310-8ba1-8eac791a3b58

src/guiengine/modaldialog.hpp

@@ -61,6 +61,9 @@ namespace GUIEngine
          */
         ModalDialog(const float percentWidth, const float percentHeight);
 
+        /** \brief Load a XML file to create the dialog from
+          * \note  This method automatically calls Widget::add() on each widget
+          */
         void loadFromFile(const char* xmlFile);
 
         virtual void onEnterPressedInternal();