Adding documentation for link object

Change-Id: Ied40e45296fb25b7efd227e2e13a2af48223ba1b
diff --git a/index.rst b/index.rst
index 1fb1b6e..b6b4df2 100644
--- a/index.rst
+++ b/index.rst
@@ -10,6 +10,7 @@
    interest
    data
    signature
+   link
    types
    changelog
    :maxdepth: 3