Update boolean.rst

Author: giormala

doc/source/user_guide/boolean.rst

@@ -41,8 +41,8 @@ If you create a column of ``NA`` values (for example to fill them later)
 with ``df['new_col'] = pd.NA``, the ``dtype`` would be set to ``object`` in the
 new column. The performance on this column will be worse than with
 the appropriate type. It's better to use
-``df['new_col'] = pd.Series(pd.NA, dtype=Int64)``
-(or another ``dtype`` as you desire).
+``df['new_col'] = pd.Series(pd.NA, dtype='Int64')``
+(or another ``dtype`` that supports ``NA``).
 
 .. ipython:: python
    df = pd.DataFrame()