Updates README to warn GHC 9 support situation

Author: konn

README.md

@@ -140,7 +140,7 @@ ghcup install hls
 If you are using [`chocolatey`](https://chocolatey.org/) to manage your installations in windows, [you can install `haskell-language-server`](https://community.chocolatey.org/packages/haskell-language-server) with
 ```
 choco install haskell-language-server
-```` 
+````
 
 ### Visual Studio Code
 
@@ -703,6 +703,11 @@ args = ["--lsp"]
 
 ## Known limitations
 
+### Limited GHC 9 Support
+Currently, GHC 9 support in HLS is in beta stage; some features are unavailable with GHC >= 9.0.1 for the time being.
+This situation is expected to be resolved in the near future after all the dependent packages support GHC 9.
+See issue [#297](https://github.com/haskell/haskell-language-server/issues/297) for the supported features in GHC 9 and the status of migration progress.
+
 ### Preprocessor
 HLS is not yet able to find project preprocessors, which may result in `could not execute: <preprocessor>` errors. This problem is
 tracked in https://github.com/haskell/haskell-language-server/issues/176 and originally comes from https://github.com/mpickering/hie-bios/issues/125