[Runtime] List Fulgens as backer of version 6.1

Author: nicolas-grekas

README.md

@@ -3,6 +3,17 @@ Runtime Component
 
 Symfony Runtime enables decoupling applications from global state.
 
+Sponsor
+-------
+
+The Runtime component for Symfony 6.1 is [backed][1] by [Fulgens][2].
+
+Fulgens is a human-sized company founded in 2018. Specialized in development, we
+provide support, analysis and training. Symfony being at the heart of our work,
+we are committed to contribute to its development at our own scale.
+
+Help Symfony by [sponsoring][3] its development!
+
 Resources
 ---------
 
@@ -11,3 +22,7 @@ Resources
  * [Report issues](https://github.com/symfony/symfony/issues) and
    [send Pull Requests](https://github.com/symfony/symfony/pulls)
    in the [main Symfony repository](https://github.com/symfony/symfony)
+
+[1]: https://symfony.com/backers
+[2]: https://fulgens.be
+[3]: https://symfony.com/sponsor