Add a comment to make the purpose more clearly

Signed-off-by: zydxhs <johnsmithcry@163.com>

exercises/error_handling/errors1.rs

@@ -36,6 +36,7 @@ mod tests {
     fn explains_why_generating_nametag_text_fails() {
         assert_eq!(
             generate_nametag_text("".into()),
+            // Don't change this line
             Err("`name` was empty; it must be nonempty.".into())
         );
     }