Mention that ini_handler "section" and "name" can't be modified

Author: benhoyt

ini.h

@@ -51,7 +51,8 @@ extern "C" {
 
    Note that even though the value parameter has type "const char*", the user
    may cast to "char*" and modify its content, as the value is not used again
-   after the call to ini_handler.
+   after the call to ini_handler. This is not true of section and name --
+   those must not be modified.
 */
 #if INI_HANDLER_LINENO
 typedef int (*ini_handler)(void* user, const char* section,