Clarify file-closing example in tutorial (GH-11652)



diff --git a/Doc/tutorial/inputoutput.rst b/Doc/tutorial/inputoutput.rst
index 7942786..fc2bd55 100644
--- a/Doc/tutorial/inputoutput.rst
+++ b/Doc/tutorial/inputoutput.rst
@@ -322,6 +322,8 @@
 
     >>> with open('workfile') as f:
     ...     read_data = f.read()
+
+    >>> # We can check that the file has been automatically closed.
     >>> f.closed
     True