Remind future maintainers to update the docs when changing CLI usage

We have a copy of the output from running just "terraform" in a page on
the website. It doesn't necessarily need to be kept 100% up to date, since
users can always run the command to get the result from the horses mouth,
but it's nice to keep it somewhat up-to-date to reduce use confusion.

commands.go

@@ -35,6 +35,12 @@ func init() {
 		Ui:          Ui,
 	}
 
+	// The command list is included in the terraform -help
+	// output, which is in turn included in the docs at
+	// website/source/docs/commands/index.html.markdown; if you
+	// add, remove or reclassify commands then consider updating
+	// that to match.
+
 	PlumbingCommands = map[string]struct{}{
 		"state": struct{}{}, // includes all subcommands
 		"debug": struct{}{}, // includes all subcommands

help.go

@@ -28,6 +28,9 @@ func helpFunc(commands map[string]cli.CommandFactory) string {
 		}
 	}
 
+	// The output produced by this is included in the docs at
+	// website/source/docs/commands/index.html.markdown; if you
+	// change this then consider updating that to match.
 	helpText := fmt.Sprintf(`
 Usage: terraform [--version] [--help] <command> [args]