Move status_url to webapp config section

This is the last entry standing in the 'zuul' section, it seems
like it may be more appropriate here.

Change-Id: I48d2c4d69025a93a61c4d4fc64574545e3215e2c
diff --git a/doc/source/admin/components.rst b/doc/source/admin/components.rst
index b91e7e7..a24b833 100644
--- a/doc/source/admin/components.rst
+++ b/doc/source/admin/components.rst
@@ -54,18 +54,14 @@
 zookeeper
 """""""""
 
+.. NOTE: this is a white lie at this point, since only the scheduler
+   uses this, however, we expect other components to use it later, so
+   it's reasonable for admins to plan for this now.
+
 **hosts**
   A list of zookeeper hosts for Zuul to use when communicating with
   Nodepool.  ``hosts=zk1.example.com,zk2.example.com,zk3.example.com``
 
-zuul
-""""
-
-**status_url**
-  URL that will be posted in Zuul comments made to changes when
-  starting jobs for a change.  Used by zuul-scheduler only.
-  ``status_url=https://zuul.example.com/status``
-
 
 Scheduler
 ---------
@@ -126,6 +122,11 @@
   optional value and ``1`` is used by default.
   ``status_expiry=1``
 
+**status_url**
+  URL that will be posted in Zuul comments made to changes when
+  starting jobs for a change.  Used by zuul-scheduler only.
+  ``status_url=https://zuul.example.com/status``
+
 scheduler
 """""""""