Move tenant_config option to scheduler section

This is only used by the scheduler and makes more sense here.

Change-Id: I85009894fd5bd02e8795d59ea2a2612b46941718
diff --git a/doc/source/admin/quick-start.rst b/doc/source/admin/quick-start.rst
index 780496b..9993775 100644
--- a/doc/source/admin/quick-start.rst
+++ b/doc/source/admin/quick-start.rst
@@ -54,7 +54,7 @@
 
 **zuul.conf**::
 
-    [zuul]
+    [scheduler]
     tenant_config=/etc/zuul/main.yaml
 
     [gearman_server]