Fix two typos on zuul documentation

ar   => are
addtion => addition

Change-Id: I93e3016b0667b7dd2f81d526b52cae4cba9e89c2
diff --git a/NEWS.rst b/NEWS.rst
index bd09bfe..5fef40a 100644
--- a/NEWS.rst
+++ b/NEWS.rst
@@ -33,7 +33,7 @@
   matches all jobs).
 
 * Multiple triggers are now supported (currently Gerrit and a simple
-  Timer trigger ar supported).  Your layout.yaml file will need to
+  Timer trigger are supported).  Your layout.yaml file will need to
   change to add the key "gerrit:" inside of the "triggers:" list to
   specify a Gerrit trigger (and facilitate adding other kinds of
   triggers later).  See the sample layout.yaml and Zuul section of the