docs(readme): update nix instructions (#359)

README.md

@@ -32,11 +32,26 @@ npm install -g @charmland/crush
 
 # Arch Linux (btw)
 yay -S crush-bin
-
-# Nix
-nix-shell -p nur.repos.charmbracelet.crush
 ```
 
+<details>
+<summary><strong>Nix</strong></summary>
+    
+Crush is available via [NUR](https://github.com/nix-community/NUR) in `nur.repos.charmbracelet.crush`.
+
+You can also try out Crush via `nix-shell`:
+
+```bash
+# Add the NUR channel.
+nix-channel --add https://github.com/nix-community/NUR/archive/main.tar.gz nur
+nix-channel --update
+
+# Get Crush in a Nix shell.
+nix-shell -p '(import <nur> { pkgs = import <nixpkgs> {}; }).repos.charmbracelet.crush'
+```
+
+</details>
+
 <details>
 <summary><strong>Debian/Ubuntu</strong></summary>
 
@@ -71,7 +86,7 @@ Or, download it:
 
 [releases]: https://github.com/charmbracelet/crush/releases
 
-Or just install it with go:
+Or just install it with Go:
 
 ```
 go install github.com/charmbracelet/crush@latest