DOC: filter method example is more clear (#32690)

Author: epizzigoni

pandas/core/generic.py

@@ -4558,6 +4558,10 @@ def filter(
         >>> df = pd.DataFrame(np.array(([1, 2, 3], [4, 5, 6])),
         ...                   index=['mouse', 'rabbit'],
         ...                   columns=['one', 'two', 'three'])
+        >>> df
+                one  two  three
+        mouse     1    2      3
+        rabbit    4    5      6
 
         >>> # select columns by name
         >>> df.filter(items=['one', 'three'])