Merge pull request 'Put flake instructions in a <details> block' (#13) from condense-readme into main

Reviewed-on: https://codeberg.org/svenvanheugten/git-check-assertions/pulls/13

README.md

@@ -19,6 +19,9 @@ On most systems, clone this repository and add the `bin` directory to your `PATH
 
 If you use Nix with flakes, you can simply add it to your program's devshell instead:
 
+<details>
+<summary>Instructions for using the flake</summary>
+
 ```diff
 @@ -2,12 +2,18 @@
    inputs = {
@@ -49,6 +52,7 @@ If you use Nix with flakes, you can simply add it to your program's devshell ins
        }
      )
 ```
+</details>
 
 ## What do you put in your commit messages?