cmd/cue: provide initial text for 'help embed'

Provide skeleton text for 'cue help embed'. This gives a one-liner that
will mirror the headline sentence from the proposal linked from
https://cuelang.org/discussion/3264.

For #3268.

Signed-off-by: Paul Jolly <[email protected]>
Change-Id: Ib511ae846c40e4eee0847190d2764ecc7401d8c8
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1197335
Reviewed-by: Roger Peppe <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>

cmd/cue/cmd/help.go

@@ -96,6 +96,7 @@ func newHelpCmd(c *Command) *cobra.Command {
 
 var helpTopics = []*cobra.Command{
 	commandsHelp,
+	embedHelp,
 	environmentHelp,
 	filetypeHelp,
 	flagsHelp,
@@ -171,6 +172,21 @@ $ cue export data.json schema: schema.json
 `,
 }
 
+var embedHelp = &cobra.Command{
+	Use:   "embed",
+	Short: "file embedding",
+	Long: `
+The @embed directive can be used to load files of any type as part of CUE
+evaluation.
+
+Note: support for embed is experimental, and is enabled via
+CUE_EXPERIMENT=embed.
+
+For more details and discussion, see the proposal linked from
+https://cuelang.org/dicsussion/3264.
+`[1:],
+}
+
 var environmentHelp = &cobra.Command{
 	Use:   "environment",
 	Short: "environment variables",

cmd/cue/cmd/testdata/script/help.txtar

@@ -105,6 +105,7 @@ Flags:
 
 Additional help topics:
   cue commands       user-defined commands
+  cue embed          file embedding
   cue environment    environment variables
   cue filetypes      supported file types and qualifiers
   cue flags          common flags for composing packages