Issue #26029: Finish correction.

Doc/extending/building.rst

@@ -81,7 +81,7 @@ In the :file:`setup.py`, all execution is performed by calling the ``setup``
 function. This takes a variable number of keyword arguments, of which the
 example above uses only a subset. Specifically, the example specifies
 meta-information to build packages, and it specifies the contents of the
-package.  Normally, a package will contain addition modules, like Python
+package.  Normally, a package will contain additional modules, like Python
 source modules, documentation, subpackages, etc. Please refer to the distutils
 documentation in :ref:`distutils-index` to learn more about the features of
 distutils; this section explains building extension modules only.