docs: fixed ascii based folder strucure in dev.md (#461)

docs/dev.md

@@ -29,8 +29,11 @@ For any URL you visit that doesn't have a corresponding page, the `400.astro` fi
 
 This is a custom **500** status code page. You can add this route by adding a page component to your `src/pages` folder:
 
-```astro
-├── src/ │ ├── components/ │ └── pages/ │ └── 500.astro
+```
+├── src/ 
+│   ├── components/ 
+│   └── pages/ 
+│       └── 500.astro
 ```
 
 This page is used any time an error occurs in the dev server.