build: ensure consistent help messages for experimental cli help

Append an [experimental] tag to the end of each experimental command to
highlight that these are experimental options. Square brackets are used
instead of parentheses as parentheses are already in use to highlight
examples and defaults.

Signed-off-by: Justin Chadwell <me@jedevc.com>

commands/build.go

@@ -479,7 +479,7 @@ func buildCmd(dockerCli command.Cli, rootOpts *rootOptions) *cobra.Command {
 	flags.StringArrayVar(&options.platforms, "platform", platformsDefault, "Set target platform for build")
 
 	if isExperimental() {
-		flags.StringVar(&options.printFunc, "print", "", "Print result of information request (outline, targets)")
+		flags.StringVar(&options.printFunc, "print", "", "Print result of information request (e.g., outline, targets) [experimental]")
 	}
 
 	flags.BoolVar(&options.exportPush, "push", false, `Shorthand for "--output=type=registry"`)
@@ -501,7 +501,7 @@ func buildCmd(dockerCli command.Cli, rootOpts *rootOptions) *cobra.Command {
 	flags.Var(options.ulimits, "ulimit", "Ulimit options")
 
 	if isExperimental() {
-		flags.StringVar(&options.invoke, "invoke", "", "Invoke a command after the build. BUILDX_EXPERIMENTAL=1 is required.")
+		flags.StringVar(&options.invoke, "invoke", "", "Invoke a command after the build [experimental]")
 	}
 
 	// hidden flags