Add period to end of sentence.

Co-authored-by: Christophe Bedard <[email protected]>

doc/pip_and_pep_668.rst

@@ -28,7 +28,7 @@ Configure using pip.conf
 ------------------------
 
 `Pip configuration files <pip-configuration>`_ can be used to set the desired behavior.
-Pip checks for global configuration files in ``XDG_CONFIG_DIRS``, as well as ``/etc/pip.conf``
+Pip checks for global configuration files in ``XDG_CONFIG_DIRS``, as well as ``/etc/pip.conf``.
 For details on ``XDG_CONFIG_DIRS`` refer to the `XDG base directories specification <xdg-base-dirs>`_.
 If you're unsure which configuration file is in use by your system, ``/etc/pip.conf`` seems like the most generic.