You are browsing the Symfony 4 documentation, which changes significantly from Symfony 3.x. If your app doesn't use Symfony 4 yet, browse the Symfony 3.4 documentation.
Contributing to Symfony
This part of the documentation tells you everything you want to know about how you can be involved with the Symfony project; from contributing documentation to fix bugs.
This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.