cmd/help: fix example in doc

Closes #468
https://github.com/cuelang/cue/pull/468

GitOrigin-RevId: df8fd25f7dc2a3b908b871778d26f3a27936e01a
Change-Id: I29bc6f9a8686f3b763825061ab023bfde15705f5
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/7102
Reviewed-by: CUE cueckoo <cueckoo@gmail.com>
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>
diff --git a/cmd/cue/cmd/cmd.go b/cmd/cue/cmd/cmd.go
index fcc1838..8998a3a 100644
--- a/cmd/cue/cmd/cmd.go
+++ b/cmd/cue/cmd/cmd.go
@@ -119,7 +119,7 @@
 		}
 
 		// starts after echo
-		file.Append & {
+		append: file.Append & {
 			filename: var.file
 			contents: echo.stdout
 		}
diff --git a/cmd/cue/cmd/help.go b/cmd/cue/cmd/help.go
index 91f3ac3..399d545 100644
--- a/cmd/cue/cmd/help.go
+++ b/cmd/cue/cmd/help.go
@@ -423,7 +423,7 @@
 		}
 
 		// starts after echo
-		file.Append & {
+		append: file.Append & {
 			filename: var.file
 			contents: echo.stdout
 		}
diff --git a/cmd/cue/cmd/testdata/script/help_cmd.txt b/cmd/cue/cmd/testdata/script/help_cmd.txt
index 9451307..d357539 100644
--- a/cmd/cue/cmd/testdata/script/help_cmd.txt
+++ b/cmd/cue/cmd/testdata/script/help_cmd.txt
@@ -116,7 +116,7 @@
 		}
 
 		// starts after echo
-		file.Append & {
+		append: file.Append & {
 			filename: var.file
 			contents: echo.stdout
 		}