gh-106318: Add an example for str.capitalize() (GH-134272)

Co-authored-by: Adorilson Bezerra <adorilson@gmail.com>
Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

Author: 3 people

Doc/builtins/stdtypes.rst

@@ -2129,13 +2129,23 @@ expression support in the :mod:`re` module).
 .. method:: str.capitalize()
 
    Return a copy of the string with its first character capitalized and the
-   rest lowercased.
+   rest lowercased. For example:
+
+   .. doctest::
+
+      >>> 'PYTHON IS AMAZING'.capitalize()
+      'Python is amazing'
+      >>> 'Njemačka starts With a non-ASCII digraph'.capitalize()
+      'Njemačka starts with a non-ascii digraph'
+
+   See also :meth:`title`.
 
    .. versionchanged:: 3.8
       The first character is now put into titlecase rather than uppercase.
       This means that characters like digraphs will only have their first
       letter capitalized, instead of the full character.
 
+
 .. method:: str.casefold()
 
    Return a casefolded copy of the string. Casefolded strings may be used for