fix 21.0.0 release announcement

This installs a forward to prevent links to the announcement from
becoming dead after the rename.

config.yml

@@ -8,7 +8,7 @@ disableKinds:
 params:
   DocsURL: https://docs.mesa3d.org
   GitLabURL: https://gitlab.freedesktop.org/mesa/mesa3d.org
-  LatestVersion: 21.0
+  LatestVersion: 21.0.0
 
 menu:
   main:

content/news/releases/mesa-21-0-0-is-released.md

+---
+title:    "Mesa 21.0.0 is released"
+date:     2021-03-11 16:45:24
+category: releases
+tags:     []
+aliases:  [/news/releases/mesa-21-0-is-released/]
+---
+[Mesa 21.0.0](https://docs.mesa3d.org/relnotes/21.0.0.html) is released. This is a new development release. See the release notes for more information about this release.

content/news/releases/mesa-21-0-is-released.md

----
-title:    "Mesa 21.0 is released"
-date:     2021-03-11 16:45:24
-category: releases
-tags:     []
----
-[Mesa 21.0](https://docs.mesa3d.org/relnotes/21.0.0.html) is released. This is a new development release. See the release notes for more information about this release.