Resolve issue with vendor folder permissions (laravel#6965)

Resolve issue with vendor folder permissions for existing application. Currently the vendor folder is created under the root user. Fixed it to install under the current system user

sail.md

@@ -141,6 +141,7 @@ You may install the application's dependencies by navigating to the application'
 
 ```nothing
 docker run --rm \
+    -u "$(id -u):$(id -g)" \
     -v $(pwd):/opt \
     -w /opt \
     laravelsail/php80-composer:latest \