api: add a comment about settings lifetime

See: #55 (comment)

Author: indutny

src/native/api.h

@@ -44,7 +44,12 @@ struct llhttp_settings_s {
   llhttp_cb      on_chunk_complete;
 };
 
-/* Initialize the parser with specific type and user settings */
+/* Initialize the parser with specific type and user settings.
+ *
+ * NOTE: lifetime of `settings` has to be at least the same as the lifetime of
+ * the `parser` here. In practice, `settings` has to be either a static
+ * variable or be allocated with `malloc`, `new`, etc.
+ */
 void llhttp_init(llhttp_t* parser, llhttp_type_t type,
                  const llhttp_settings_t* settings);