docs: deprecate github mirror — moved to forgejo

Author: barrettruth

README.md

@@ -1,5 +1,10 @@
 # http-codes.nvim
 
+> [!IMPORTANT]
+> **This project has moved to <https://git.barrettruth.com/barrettruth/http-codes.nvim>.**
+> Issues, pull requests, and active development happen on Forgejo. This GitHub mirror is archived.
+> `luarocks install http-codes.nvim` continues to publish from Forgejo CI on tag push.
+
 Quickly investigate HTTP status codes with [Mozilla](https://developer.mozilla.org/en-US/docs/Web/HTTP), with telescope, fzf-lua, and snacks.nvim integrations.
 
 ## Installation