Fix typo errors in devstack documentation

This submission fixes typo errors in following files
  1. contributing.rst
  2. exerciserc.rst
  3. faq.rst
  4. local.conf.rst
  5. openrc.rst

Change-Id: I2b2d61673c3c95f60c56978b5a81016603fef252
diff --git a/doc/source/local.conf.rst b/doc/source/local.conf.rst
index b2f7557..a1ca60a 100644
--- a/doc/source/local.conf.rst
+++ b/doc/source/local.conf.rst
@@ -2,7 +2,7 @@
 local.conf - User Settings
 ==========================
 
-``local.conf`` is a user-maintained setings file that is sourced in
+``local.conf`` is a user-maintained settings file that is sourced in
 ``stackrc``. It contains a section that replaces the historical
 ``localrc`` file. See the description of
 :doc:`local.conf <configuration>` for more details about the mechanics