Add completion hints to maintained commands

docs/consumers/guide.md

@@ -87,6 +87,34 @@ values convert before input construction. A command's `NewInput` creates input
 only when execution reaches it; help does not construct caller input or run
 provider callbacks.
 
+## Shell completion
+
+Install `commandkit.Completion("app")` alongside the application's other
+declarations, using the basename operators actually type. The basename accepts
+letters, digits, underscores, dots, hyphens, and colons, except for a leading
+hyphen. Add a hint to a flag or operand's metadata when a value has useful
+static choices or is a filesystem path:
+
+```go
+commandkit.FlagMeta{
+	Name: "format",
+	Completion: commandkit.CompleteChoices(
+		commandkit.CompletionChoice{Value: "text", Description: "Readable text"},
+		commandkit.CompletionChoice{Value: "yaml", Description: "YAML output"},
+	),
+}
+commandkit.FlagMeta{Name: "config", Completion: commandkit.CompleteFiles()}
+commandkit.ArgumentMeta{Name: "directory", Completion: commandkit.CompleteDirectories()}
+```
+
+Hints are suggestions: converters and input validation still decide which
+values are accepted. An omitted hint or `NoCompletion()` gives no value
+suggestions. `CompleteChoices()` with no choices also gives no suggestions.
+Declarations retain copies of supplied choices. The [CLI reference](../cli.md#shell-completion)
+describes supported shells and loading scripts; the [core example](../../examples/core)
+and [composed example](../../integrations/ckprompt/examples/composed) show
+installation alongside aliases and integration commands.
+
 ## Invocation reporting
 
 `Invocation.Reporter()` supplies the reporter for the current handler. Use