website/docs: added info about how to upgrade (#5589)

added info about how to upgrade

Co-authored-by: Tana Berry <tana@goauthentik.io>

website/docs/installation/index.md

@@ -0,0 +1,9 @@
+---
+title: Installation
+---
+
+Everything you need to get authentik up and running! For information about upgrading to a new version, refer to the <b>Upgrade</b> section in the relevant [Release Notes](../releases).
+
+import DocCardList from '@theme/DocCardList';
+
+<DocCardList />

website/sidebars.js

@@ -9,11 +9,8 @@ module.exports = {
             label: "Installation",
             collapsed: false,
             link: {
-                type: "generated-index",
+                type: "doc",
-                title: "Installation",
+                id: "installation/index",
-                slug: "installation",
-                description:
-                    "Everything you need to get authentik up and running!",
             },
             items: [
                 "installation/docker-compose",