Add DRAFT change state to JSON documentation

Change-Id: Ia13b3c8f2d6e02aa5d1388e25f517ba3f49f2ff2

Documentation/json.txt

diff --git a/Documentation/json.txt b/Documentation/json.txt
index c7b49b9..3659ed3 100644
--- a/Documentation/json.txt
+++ b/Documentation/json.txt
@@ -44,6 +44,8 @@
 
   NEW;; Change is still being reviewed.
 
+  DRAFT;; Change is a draft change that only consists of draft patchsets.
+
   SUBMITTED;; Change has been submitted and is in the merge queue.
   It may be waiting for one or more dependencies.