Using mg_connection::callback_param for mg_iterate_over_connection()

docs/API.md

@@ -131,9 +131,9 @@ is returned.
 This is an interface primarily designed to push arbitrary data to websocket
 connections at any time. This function could be called from the IO thread only.
 When it returns, an IO thread calls `func()` on each active connection,
-passing `param` as an extra parameter. It is allowed to call `mg_send_data()` or
-`mg_websocket_write()` within a callback, cause `func` is executed in the
-context of the IO thread.
+passing `param` as `struct mg_connection::callback_param`.
+It is allowed to call `mg_send_data()` or `mg_websocket_write()` within a
+callback, cause `func` is executed in the context of the IO thread.
 
     void mg_send_status(struct mg_connection *, int status_code);
     void mg_send_header(struct mg_connection *, const char *name,