Doc: Introduce changelog for 1.0 release

Signed-off-by: Soby Mathew <soby.mathew@arm.com>
Change-Id: I0ae8d3a1fe64ada327ba8f95496657633a16160c
diff --git a/docs/index.rst b/docs/index.rst
index 6ca8c95..f360584 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -18,6 +18,7 @@
 
     Home<docs/readme>
     docs/about/index
+    docs/changelog
     docs/design_documents/index
     docs/user_guides/index
     docs/processes/index