nix: refactor with flakes

README.md

@@ -78,6 +78,7 @@ background](https://neilmitchell.blogspot.com/2020/01/one-haskell-ide-to-rule-th
       - [Using Cabal](#using-cabal)
       - [Using Stack](#using-stack)
       - [Using Nix](#using-nix)
+        - [Flakes support](#flakes-support)
       - [Introduction tutorial](#introduction-tutorial)
       - [Test your hacked HLS in your editor](#test-your-hacked-hls-in-your-editor)
     - [Adding support for a new editor](#adding-support-for-a-new-editor)
@@ -807,8 +808,25 @@ $ cabal update
 $ cabal build
 ```
 
+##### Flakes support
+
+If you are using nix 2.4 style command (enabled by `experimental-features = nix-command`),
+you can use `nix develop` instead of `nix-shell` to enter the development shell. To enter the shell with specific GHC versions:
+
+* `nix develop` or `nix develop #haskell-language-server-dev` - default GHC version
+* `nix develop #haskell-language-server-8104-dev` - GHC 8.10.4
+* `nix develop #haskell-language-server-884-dev` - GHC 8.8.4
+* `nix develop #haskell-language-server-901-dev` - GHC 9.0.1
+
 If you are looking for a Nix expression to create haskell-language-server binaries, see https://github.com/haskell/haskell-language-server/issues/122
 
+To create binaries:
+
+* `nix build` or `nix build #haskell-language-server` - default GHC version
+* `nix build #haskell-language-server-8104` - GHC 8.10.4
+* `nix build #haskell-language-server-884` - GHC 8.8.4
+* `nix build #haskell-language-server-901` - GHC 9.0.1
+
 #### Introduction tutorial
 
 Pepeiborra [wrote an tutorial](https://github.com/pepeiborra/hls-tutorial) on writing a plugin in HLS.