gh-46236: Document PyUnicodeIter_Type (GH-132925)

Author: StanFromIreland

Doc/c-api/unicode.rst

@@ -33,8 +33,14 @@ Python:
 
 .. c:var:: PyTypeObject PyUnicode_Type
 
-   This instance of :c:type:`PyTypeObject` represents the Python Unicode type.  It
-   is exposed to Python code as :py:class:`str`.
+   This instance of :c:type:`PyTypeObject` represents the Python Unicode type.
+   It is exposed to Python code as :py:class:`str`.
+
+
+.. c:var:: PyTypeObject PyUnicodeIter_Type
+
+   This instance of :c:type:`PyTypeObject` represents the Python Unicode
+   iterator type. It is used to iterate over Unicode string objects.
 
 
 .. c:type:: Py_UCS4