[master] 104c593 document the default probe

[Nils Goroll]

commit 104c5930a6fdfe23416d3d20d77664c3b9aee793
Author: Nils Goroll <nils.goroll at uplex.de>
Date:   Wed May 11 16:14:17 2016 +0200

    document the default probe

diff --git a/doc/sphinx/reference/vcl.rst b/doc/sphinx/reference/vcl.rst
index b8650f6..7e73504 100644
--- a/doc/sphinx/reference/vcl.rst
+++ b/doc/sphinx/reference/vcl.rst
@@ -244,6 +244,9 @@ the backend as down it they fail. A probe is defined as this::
         .attribute = "value";
     }
 
+The probe named `default` is special and will be used for all backends
+which do not explicitly reference a probe.
+
 There are no mandatory options. These are the options you can set:
 
   url