fix: Quick Demo example shell quoting (#4285)

Author: notpeter

docs/index.md

@@ -58,7 +58,7 @@ Project setup is a breeze with Pixi.
 pixi init hello-world
 cd hello-world
 pixi add python
-pixi run python -c "print('Hello World!')"
+pixi run python -c 'print("Hello World!")'
 ```
 
 ![Pixi Demo](assets/vhs-tapes/pixi_project_demo_light.gif#only-light)