docs: update installation docs to include frontend asset build (#23199)

docs/docs/installation/installing-superset-from-scratch.mdx

@@ -138,6 +138,12 @@ superset load_examples
 # Create default roles and permissions
 superset init
 
+# Build javascript assets
+cd superset-frontend
+npm ci
+npm run build
+cd ..
+
 # To start a development web server on port 8088, use -p to bind to another port
 superset run -p 8088 --with-threads --reload --debugger
 ```