chore: add contributing details

CONTRIBUTING.md

@@ -38,10 +38,19 @@ Alternatively, you can also work with the test application we provide:
     cd tests/Fixtures/app
     ./console assets:install --symlink
     symfony serve
+
+    # if you prefer keeping the server in your terminal:
+    symfony server:start --dir tests/Fixtures/app
 
     # or if you prefer using the PHP built-in web server
     php -S localhost:8000 -t public/
 
+You also have access to a `console`:
+
+```
+APP_DEBUG=1 tests/Fixtures/app/console debug:config
+```
+
 ### Matching Coding Standards
 
 The API Platform project follows [Symfony coding standards](https://symfony.com/doc/current/contributing/code/standards.html).