Add a note about what a missing const specifier does mean in the context

of the request_info structure.

main/SAPI.h

@@ -59,6 +59,11 @@ typedef struct _sapi_module_struct sapi_module_struct;
 
 extern sapi_module_struct sapi_module;  /* true global */
 
+/* Some values in this structure needs to be field in before
+ * calling sapi_activate(). We WILL change the `char *' entries,
+ * so make sure that you allocate a separate buffer for them
+ * and that you free them after sapi_deactivate().
+ */
 
 typedef struct {
 	const char *request_method;