Clarify docs re mode's octal representation (#44410)

* Clarify docs re mode's octal representation

I changed the language about how to use mode to make it more obvious
that using "01777" is not a typo, because the leading zero is not meant
to reflect the way that number might have been given on a command line.
See also: issues #5409 #9196 #11385 #13115 #18952 #23491 #23521

lib/ansible/modules/files/file.py

@@ -103,11 +103,12 @@ options:
 '''
 
 EXAMPLES = '''
-# change file ownership, group and mode. When specifying mode using octal numbers, first digit should always be 0.
+# change file ownership, group and mode
 - file:
     path: /etc/foo.conf
     owner: foo
     group: foo
+    # when specifying mode using octal numbers, add a leading 0
     mode: 0644
 - file:
     path: /work