Add an example of filter in documentation

[filter "-status:draft"] to express
"Do not add reviewers to drafts".

Change-Id: I78aa4f2534924f913856653db2af5c1bd59aed4a
diff --git a/src/main/resources/Documentation/config.md b/src/main/resources/Documentation/config.md
index 0f0693b..6782350 100644
--- a/src/main/resources/Documentation/config.md
+++ b/src/main/resources/Documentation/config.md
@@ -36,6 +36,8 @@
   [filter "branch:stable-2.10"]
     reviewer = QAGroup
 
+  [filter "-status:draft"]
+    reviewer = DevGroup
 ```
 
 filter.\<filter\>.reviewer