README: mention ghc-9.6.6 branch

README.md

@@ -10,8 +10,6 @@ University of Helsinki
 
 This work is licensed under a [Creative Commons Attribution-ShareAlike 4.0 International License](https://creativecommons.org/licenses/by-sa/4.0/).
 
-_New!_ Exercise repository updated to use GHC 9.2.8! You'll need to rerun `stack build`.
-
 ## About the course
 
 This is an online course on Functional Programming that uses the
@@ -52,6 +50,14 @@ Here are some fixes for common problems with `stack build`:
 - If you get an error like `While building package zlib-0.6.2.3`, you need to install the zlib library headers. The right command for Ubuntu is `sudo apt install zlib1g-dev`.
 - If you get an error like `Downloading lts-18.18 build plan ... RedownloadInvalidResponse`, your version of stack is too old. Run `stack upgrade` to get a newer one.
 
+### Newer GHC version
+
+If you need to use a newer version of GHC, perhaps to get
+vscode-haskell to work, try the `ghc-9.6.6` branch of this repository
+for GHC 9.6.6. The default for the course is GHC 9.2.8 for now.
+
+Don't forget to run `stack build` again after changing branches.
+
 ## Reporting errors
 
 If you notice an error in these materials, you can report it via