gh-106318: Add example for str.isalpha()

Doc/library/stdtypes.rst

@@ -1990,6 +1990,18 @@
    from the `Alphabetic property defined in the section 4.10 'Letters, Alphabetic, and
    Ideographic' of the Unicode Standard
    <https://www.unicode.org/versions/Unicode16.0.0/core-spec/chapter-4/#G91002>`_.
+   For example:
+
+   .. doctest::
+
+      >>> 'a commom word'.isalpha()
+      False
+      >>> 'acommomword'.isalpha()
+      True
+      >>> 'µ'.isalpha() # no-ascii characters could be alpha too
+      True
+
+   See :ref:`unicode-properties`.
 
 
 .. method:: str.isascii()