Release 6.1 documentation

Change-Id: I850bcdc77a096df51248640dfaf6e72aa7225001
diff --git a/book.json b/book.json
index 83cd6ad..ad7d67a 100644
--- a/book.json
+++ b/book.json
@@ -8,7 +8,7 @@
     "website": "styles/website.css"
   },
   "variables": {
-    "branch": "master"
+    "branch": "cord-6.1"
   },
   "plugins": [
     "anchorjs",
@@ -30,6 +30,10 @@
           "text": "Master (Devel)"
         },
         {
+          "value": "/cord-6.1",
+          "text": "6.1 (Stable)"
+        },
+        {
           "value": "/cord-6.0",
           "text": "6.0 (Stable)"
         },