put gist in core commands

pkg/cmd/gist/gist.go

@@ -1,6 +1,7 @@
 package gist
 
 import (
+	"github.com/MakeNowJust/heredoc"
 	gistCreateCmd "github.com/cli/cli/pkg/cmd/gist/create"
 	gistEditCmd "github.com/cli/cli/pkg/cmd/gist/edit"
 	gistListCmd "github.com/cli/cli/pkg/cmd/gist/list"
@@ -14,6 +15,14 @@ func NewCmdGist(f *cmdutil.Factory) *cobra.Command {
 		Use:   "gist",
 		Short: "Create gists",
 		Long:  `Work with GitHub gists.`,
+		Annotations: map[string]string{
+			"IsCore": "true",
+			"help:arguments": heredoc.Doc(`
+				A gist can be supplied as argument in any of the following formats:
+				- by ID, e.g. 5b0e0062eb8e9654adad7bb1d81cc75f
+				- by URL, e.g. "https://gist.github.com/OWNER/5b0e0062eb8e9654adad7bb1d81cc75f"; or
+			`),
+		},
 	}
 
 	cmd.AddCommand(gistCreateCmd.NewCmdCreate(f, nil))