doc: note a gotcha with http.Server sockets

doc/api/http.markdown

@@ -64,8 +64,10 @@ per connection (in the case of keep-alive connections).
 `function (socket) { }`
 
  When a new TCP stream is established. `socket` is an object of type
- `net.Socket`. Usually users will not want to access this event. The
- `socket` can also be accessed at `request.connection`.
+ `net.Socket`. Usually users will not want to access this event. In
+ particular, the socket will not emit `readable` events because of how
+ the protocol parser attaches to the socket. The `socket` can also be
+ accessed at `request.connection`.
 
 ### Event: 'close'