docs(src): add examples alias and general cleanup (#2763)

src/upnp.h

@@ -1,11 +1,14 @@
 /**
  * @file src/upnp.h
- * @brief todo
+ * @brief Declarations for UPnP port mapping.
  */
 #pragma once
 
 #include "platform/common.h"
 
+/**
+ * @brief UPnP port mapping.
+ */
 namespace upnp {
   [[nodiscard]] std::unique_ptr<platf::deinit_t>
   start();