Point to phosphor-dbus-interfaces repo

dbus-interfaces.md was removed here:
https://github.com/openbmc/docs/commit/d9c32b0762dede747a6bc42b9f997027ce5b5955
and before was moved to the deprecated dir, so this link hasn't
worked for some time. It should point to phosphor-dbus-interfaces
repo instead.

Change-Id: I87e21d593a785e94cf07f3b58eaf32212681db70
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index d6dfc43..0ec880d 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -265,11 +265,11 @@
  * Type signatures should and use the simplest types possible, appropriate
    for the data passed. For example, don't pass numbers as ASCII strings.
 
- * New D-Bus interfaces should be documented in the 'docs' repository, at:
+ * D-Bus interfaces are defined in the `phosphor-dbus-interfaces` repository at:
 
-     https://github.com/openbmc/docs/blob/master/dbus-interfaces.md
+     https://github.com/openbmc/phosphor-dbus-interfaces
 
-See also: http://dbus.freedesktop.org/doc/dbus-api-design.html
+See: http://dbus.freedesktop.org/doc/dbus-api-design.html
 
 
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