docs: Add frontend dependency installation steps

This commit adds explicit instructions for installing frontend dependencies
and a comment for compiling translations, which were previously omitted. While these steps
might be obvious to experienced contributors, they are crucial for new users trying to set up the project for the first time.

docs/docs/contributing/howtos.mdx

@@ -579,6 +579,9 @@ a collection of JSON files. To convert all PO files to formatted JSON files you
 the build-translation script
 
 ```bash
+# Install dependencies if you haven't already
+cd superset-frontend/ && npm ci
+# Compile translations for the frontend
 npm run build-translation
 ```