doc: clarify http timeouts

Socket timeouts set using the `connection` event are replaced by
server.keepAliveTimeout when a response is handled.

Author: inversion

doc/api/http.md

@@ -901,6 +901,10 @@ also be accessed at `request.connection`.
 This event can also be explicitly emitted by users to inject connections
 into the HTTP server. In that case, any [`Duplex`][] stream can be passed.
 
+If `socket.setTimeout()` is called here, note that the timeout will
+be replaced with `server.keepAliveTimeout` when the socket has served
+a request (if `server.keepAliveTimeout` is non-zero).
+
 ### Event: 'request'
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