Fix line numbers in code block

Author: astrojuanlu

doc/tutorial/describing-code.rst

@@ -302,7 +302,7 @@ for easy examination. It is now time to fix the function:
 
 .. code-block:: python
    :caption: lumache.py
-   :emphasize-lines: 3
+   :emphasize-lines: 2
 
    def get_random_ingredients():
        return ["shells", "gorgonzola", "parsley"]