Revert "Remove preview from docs (#267)" (#270)

This reverts commit db5c3e8.

Author: benjaminhuo

config.toml

@@ -108,7 +108,7 @@ version = "0.8"
 url_latest_version = "/docs"
 
 [[params.versions]]
-  version = "v0.8"
+  version = "v0.8 (preview)"
   url = "/docs"
 
 [[params.versions]]

content/en/docs/_index.md

@@ -1,5 +1,5 @@
 ---
-title: "v0.8"
+title: "v0.8 (preview)"
 linkTitle: "Docs"
 weight: 20
 ---