Add highly visible note so that I don't ever again do the same mistake that I fix in previous commit but really puzzled me for a while :)

git-svn-id: svn+ssh://svn.code.sf.net/p/supertuxkart/code/main/trunk@9652 178a84e3-b1eb-0310-8ba1-8eac791a3b58

src/graphics/material.cpp

@@ -455,6 +455,9 @@ void Material::setSFXSpeed(SFXBase *sfx, float speed) const
  */
 void  Material::setMaterialProperties(video::SMaterial *m) const
 {
+    // !!======== This method is only called for materials that can be found in
+    //            materials.xml, if you want to set flags for all surfaces, see
+    //            'MaterialManager::setAllMaterialFlags'
     int modes = 0;
     
     if (m_alpha_testing)