gh-139580: Clarify pathlib full_match recursive pattern docs

Author: harjothkhara

Doc/library/pathlib.rst

@@ -575,6 +575,16 @@ Pure paths provide the following methods and properties:
       >>> PurePath('/a/b/c.py').full_match('**/*.py')
       True
 
+   The recursive wildcard "``**``" matches complete path segments.  Therefore
+   a pattern such as "``/a/**``" matches "``/a/b``", but not "``/a``":
+   the slash before "``**``" must also be present in the path, and path
+   objects do not preserve a trailing slash::
+
+      >>> PurePath('/a/b').full_match('/a/**')
+      True
+      >>> PurePath('/a').full_match('/a/**')
+      False
+
    .. seealso::
       :ref:`pathlib-pattern-language` documentation.