Added small note about shutdown

See https://github.com/ipfs/go-ipfs/pull/2180#issuecomment-171889567



License: MIT
Signed-off-by: Richard Littauer <richard.littauer@gmail.com>

cmd/ipfs/daemon.go

@@ -160,6 +160,7 @@ func daemonFunc(req cmds.Request, res cmds.Response) {
 		select {
 		case <-req.Context().Done():
 			fmt.Println("Received interrupt signal, shutting down...")
+			fmt.Println("(Hit ctrl-c again to force-shutdown the daemon.)")
 		}
 	}()