Update README.markdown

Author: 94noni

README.markdown

@@ -23,7 +23,7 @@ We love contributors! For more information on how you can contribute, please rea
 the [Symfony Docs Contributing Guide](https://symfony.com/doc/current/contributing/documentation/overview.html)
 
 **Important**: use `4.4` branch as the base of your pull requests, unless you are
-documenting a feature that was introduced *after* Symfony 4.4 (e.g. in Symfony 5.2).
+documenting a feature that was introduced *after* Symfony 4.4 (e.g. in Symfony 5.4).
 
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