Fix two typos on faq.rst

guarunteed => guaranteed
Centos     => CentOS

Change-Id: Id356443fcdc4128ff20d7a89158265aa16c105b2
diff --git a/doc/source/faq.rst b/doc/source/faq.rst
index 3562bfa..7aca8d0 100644
--- a/doc/source/faq.rst
+++ b/doc/source/faq.rst
@@ -54,7 +54,7 @@
 releases other than those documented in ``README.md`` on a best-effort
 basis.
 
-Are there any differences between Ubuntu and Centos/Fedora support?
+Are there any differences between Ubuntu and CentOS/Fedora support?
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 Both should work well and are tested by DevStack CI.
@@ -146,7 +146,7 @@
 
 
 Upstream DevStack is only tested with master and stable
-branches. Setting custom BRANCH definitions is not guarunteed to
+branches. Setting custom BRANCH definitions is not guaranteed to
 produce working results.
 
 What can I do about RabbitMQ not wanting to start on my fresh new VM?