Deprecate 'docker insert'

'docker insert' is an old command which predates 'docker build'. We no
longer recommend using it, it is not actively maintained, and can be
replaced with the combination of 'docker build' and 'ADD'.

This removes the command from usage and documentation, and prints a
warning when it is called.

The command still works but it will be removed in a future version.

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)

api/client/commands.go

@@ -56,7 +56,6 @@ func (cli *DockerCli) CmdHelp(args ...string) error {
 		{"images", "List images"},
 		{"import", "Create a new filesystem image from the contents of a tarball"},
 		{"info", "Display system-wide information"},
-		{"insert", "Insert a file in an image"},
 		{"inspect", "Return low-level information on a container"},
 		{"kill", "Kill a running container"},
 		{"load", "Load an image from a tar archive"},
@@ -85,7 +84,9 @@ func (cli *DockerCli) CmdHelp(args ...string) error {
 	return nil
 }
 
+// FIXME: 'insert' is deprecated.
 func (cli *DockerCli) CmdInsert(args ...string) error {
+	fmt.Fprintf(os.Stderr, "Warning: '%s' is deprecated and will be removed in a future version. Please use 'docker build' and 'ADD' instead.\n")
 	cmd := cli.Subcmd("insert", "IMAGE URL PATH", "Insert a file from URL in the IMAGE at PATH")
 	if err := cmd.Parse(args); err != nil {
 		return nil