Fix mongoose docs generation

PUBLISHED_FROM=331821dcd1f7dc8a94581cd8a9b51aa00a89fddc

docs/c-api/mg_http.h/mg_printf_websocket_frame.md

@@ -0,0 +1,14 @@
+---
+title: "mg_printf_websocket_frame()"
+decl_name: "mg_printf_websocket_frame"
+symbol_kind: "func"
+signature: |
+  void mg_printf_websocket_frame(struct mg_connection *nc, int op_and_flags,
+                                 const char *fmt, ...);
+---
+
+Sends WebSocket frame to the remote end.
+
+Like `mg_send_websocket_frame()`, but allows to create formatted messages
+with `printf()`-like semantics. 
+