bpo-36345: Update wsgiref example (GH-12562)

Use literalinclude markup to include Tools/scripts/serve.py code.
Tools/scripts/serve.py first argument on the command line is now optional.
diff --git a/Tools/scripts/serve.py b/Tools/scripts/serve.py
index dae21f2..7ac9c10 100755
--- a/Tools/scripts/serve.py
+++ b/Tools/scripts/serve.py
@@ -25,11 +25,12 @@
         return [b'not found']
 
 if __name__ == '__main__':
-    path = sys.argv[1]
+    path = sys.argv[1] if len(sys.argv) > 1 else os.getcwd()
     port = int(sys.argv[2]) if len(sys.argv) > 2 else 8000
     httpd = simple_server.make_server('', port, app)
     print("Serving {} on port {}, control-C to stop".format(path, port))
     try:
         httpd.serve_forever()
     except KeyboardInterrupt:
-        print("\b\bShutting down.")
+        print("Shutting down.")
+        httpd.server_close()