Fix configuration link syntax error

The configuration guide link has syntax problem in README.rst,
and the click the link will lead to page 404.

Fix the syntax problem

Change-Id: I47a1641a6898930dca508cdac98b1b43c05dc446
diff --git a/README.rst b/README.rst
index dfa68b9..b4240bd 100644
--- a/README.rst
+++ b/README.rst
@@ -92,5 +92,5 @@
 `local.conf`.  It is likely that you will need to provide and modify
 this file if you want anything other than the most basic setup.  Start
 by reading the `configuration guide
-<https://docs.openstack.org/developer/devstack/configuration.html>_`
+<https://docs.openstack.org/developer/devstack/configuration.html>`_
 for details of the configuration file and the many available options.