Move status_url from webapp to web section

The webapp will be fully replaced by zuul-web so also move the
status_url setting there.

Change-Id: I8278d9ca81ed7b0a2a2189d42b8b69c5eea2bab5
diff --git a/doc/source/admin/drivers/github.rst b/doc/source/admin/drivers/github.rst
index 4f46af6..83ac77f 100644
--- a/doc/source/admin/drivers/github.rst
+++ b/doc/source/admin/drivers/github.rst
@@ -317,10 +317,10 @@
       reporter should set as the commit status on github.
 
    .. TODO support role markup in :default: so we can xref
-      :attr:`webapp.status_url` below
+      :attr:`web.status_url` below
 
    .. attr:: status-url
-      :default: webapp.status_url or the empty string
+      :default: web.status_url or the empty string
 
       String value for a link url to set in the github
       status. Defaults to the zuul server status_url, or the empty