doc: correct http.Server.listen()

Fixes nodejs#2325.

Author: koichik

doc/api/http.markdown

@@ -103,16 +103,18 @@ IPv4 address (`INADDR_ANY`).
 
 To listen to a unix socket, supply a filename instead of port and hostname.
 
-This function is asynchronous. The last parameter `callback` will be called
-when the server has been bound to the port.
+This function is asynchronous. The last parameter `callback` will be added as
+a listener for the ['listening'](net.html#event_listening_) event.
+See also [net.Server.listen()](net.html#server.listen).
 
 
 ### server.listen(path, [callback])
 
 Start a UNIX socket server listening for connections on the given `path`.
 
-This function is asynchronous. The last parameter `callback` will be called
-when the server has been bound.
+This function is asynchronous. The last parameter `callback` will be added as
+a listener for the ['listening'](net.html#event_listening_) event.
+See also [net.Server.listen()](net.html#server.listen).
 
 
 ### server.close()