Don't use in-line yaml lists

I typed this in irc, but it's not the way I think we should normally
use lists in yaml.

Change-Id: I0d3a3dfe4015dc8ea9f7d3957fe5de29c3e2283b

doc/source/zuulv3.rst

@@ -457,12 +457,12 @@ Periodic Jobs
 In Zuul v3 periodic jobs are just like regular jobs. So instead of
 putting ``periodic-foo-master`` and ``periodic-foo-pike`` on a
 project, you just put ``foo`` in the periodic pipeline. Zuul will then
-emits trigger events for every project-branch combination.
+emit trigger events for every project-branch combination.
 
-So, if you add a periodic job to a project, it will run on all that
-projects branches. If you only want it to run on a subset of branches,
-you just use branch matchers in the project-pipeline in the regular
-way.
+So if you add a periodic job to a project it will run on all of that
+project's branches. If you only want it to run on a subset of
+branches, just use branch matchers in the project-pipeline in the
+regular way.
 
 The following will run ``tox-py35`` on all branches in the project:
 
@@ -484,7 +484,9 @@ This example runs ``tox-py35`` only on ``master`` and
         periodic:
           jobs:
             - tox-py35:
-                branches: [master, stable/queens]
+                branches:
+                  - master
+                  - stable/queens
 
 Changes to OpenStack tox jobs
 =============================