docs: move dynamic port docs from advanced guide to TCPSite reference

Per maintainer feedback, the dynamic port binding explanation and example
is more useful in the TCPSite reference docs where users looking up
TCPSite will naturally find it, rather than buried in the advanced guide.

Author: rodrigo.nogueira

docs/web_advanced.rst

@@ -1279,27 +1279,6 @@ the middleware might use :meth:`BaseRequest.clone`.
    for modifying *scheme*, *host* and *remote* attributes according
    to ``Forwarded`` and ``X-Forwarded-*`` HTTP headers.
 
-Deploying with a dynamic port
------------------------------
-
-When deploying aiohttp with zero-configuration networking, it may be useful
-to have the server bind to a dynamic port. This can be done by
-using the ``0`` port number. This will cause the OS to assign a
-free port to the server. The assigned port can be retrieved
-using the :attr:`TCPSite.port` property after the server has started.
-
-For example::
-
-    app = web.Application()
-    runner = web.AppRunner(app)
-    await runner.setup()
-    site = web.TCPSite(runner, 'localhost', 0)
-    await site.start()
-
-    print(f"Server started on port {site.port}")
-    while True:
-        await asyncio.sleep(3600)  # sleep forever
-
 CORS support
 ------------
 

docs/web_reference.rst

@@ -2940,6 +2940,22 @@ application on specific TCP or Unix socket, e.g.::
       This attribute is only guaranteed to be correct after the server has
       been started.
 
+      When deploying aiohttp with zero-configuration networking, it may be
+      useful to have the server bind to a dynamic port. This can be done by
+      using the ``0`` port number, which causes the OS to assign a free port.
+      The assigned port can be retrieved using this attribute after the server
+      has started::
+
+          app = web.Application()
+          runner = web.AppRunner(app)
+          await runner.setup()
+          site = web.TCPSite(runner, 'localhost', 0)
+          await site.start()
+
+          print(f"Server started on port {site.port}")
+          while True:
+              await asyncio.sleep(3600)  # sleep forever
+
 
 .. class:: UnixSite(runner, path, *, \
                    shutdown_timeout=60.0, ssl_context=None, \