add 'to STDOUT' to the help, and add a simple eg that mentions it too

commands.go

@@ -1451,7 +1451,7 @@ func (cli *DockerCli) CmdEvents(args ...string) error {
 }
 
 func (cli *DockerCli) CmdExport(args ...string) error {
-	cmd := cli.Subcmd("export", "CONTAINER", "Export the contents of a filesystem as a tar archive")
+	cmd := cli.Subcmd("export", "CONTAINER", "Export the contents of a filesystem as a tar archive to STDOUT")
 	if err := cmd.Parse(args); err != nil {
 		return nil
 	}

docs/sources/commandline/cli.rst

@@ -369,7 +369,13 @@ Show events in the past from a specified time
 
     Usage: docker export CONTAINER
 
-    Export the contents of a filesystem as a tar archive
+    Export the contents of a filesystem as a tar archive to STDOUT
+    
+for example:
+
+.. code-block:: bash
+
+    $ sudo docker export red_panda > latest.tar
 
 .. _cli_history: