docs: Simplify the CONTRIBUTING file by suggesting the usage of the script to run cspell (#3725)

Simplify the CONTRIBUTING file by suggesting the usage of the script to
run cspell.

Co-authored-by: Lukas Klingsbo <me@lukas.fyi>

Author: luanpotter

CONTRIBUTING.md

@@ -114,10 +114,10 @@ you can do so using npm or yarn:
 npm install -g cspell
 ```
 
-Then you can run it with the following arguments:
+Then you can run it using the provided script:
 
 ```bash
-cspell --no-progress -c .github/cspell.json "**/*.{md,dart}"
+./scripts/cspell-run.sh
 ```