Minor comment improvement.

include/freetype/config/ftoption.h

@@ -82,6 +82,10 @@ FT_BEGIN_HEADER
   /* to control the various font drivers and modules.  The controllable    */
   /* properties are listed in the section @properties.                     */
   /*                                                                       */
+  /* You have to undefine this configuration option on platforms that lack */
+  /* the concept of environment variables (and thus don't have the         */
+  /* `getenv' function), for example Windows CE.                           */
+  /*                                                                       */
   /* `FREETYPE_PROPERTIES' has the following syntax form (broken here into */
   /* multiple lines for better readability).                               */
   /*                                                                       */