Insert "that" so that a sentence reads better.

Author: vsajip

Doc/library/venv.rst

@@ -24,7 +24,7 @@ their :mod:`site` directories.
 A virtual environment is created on top of an existing
 Python installation, known as the virtual environment's "base" Python, and by
 default is isolated from the packages in the base environment,
-so only those explicitly installed in the virtual environment are available.
+so that only those explicitly installed in the virtual environment are available.
 See :ref:`sys-path-init-virtual-environments` and :mod:`site`'s
 :ref:`virtual environments documentation <site-virtual-environments-configuration>`
 for more information.