Make minor update to 404 and topnav

Change-Id: I258afeb634a0349d8ee75fa6bdec92a42a3bef3f
diff --git a/404.md b/404.md
index a7b58c0..1e6b8af 100644
--- a/404.md
+++ b/404.md
@@ -1,6 +1,9 @@
 ---
 title: "Page Not Found"
 search: exclude
+hide_sidebar: true
+hide_navtoggle: true
+toc: false
 ---  
 
 Sorry, but the page you were trying to view does not exist. Try searching for it or looking at the URL to see if it looks correct.
diff --git a/_data/topnav.yml b/_data/topnav.yml
index 6c3b799..a7250af 100644
--- a/_data/topnav.yml
+++ b/_data/topnav.yml
@@ -16,7 +16,7 @@
         - title: Source
           external_url: https://gerrit.googlesource.com/gerrit/
         - title: Releases
-          external_url: https://www.gerritcodereview.com/releases/README.md
+          url: /releases-readme.html
         - title: Builds
           external_url: https://gerrit-ci.gerritforge.com/
         - title: Reviews