[Messenger][Process] Add SensioLabs as a backer to the README

Author: nicolas-grekas

README.md

@@ -3,6 +3,17 @@ Process Component
 
 The Process component executes commands in sub-processes.
 
+Sponsor
+-------
+
+The Process component for Symfony 5.4/6.0 is [backed][1] by [SensioLabs][2].
+
+As the creator of Symfony, SensioLabs supports companies using Symfony, with an
+offering encompassing consultancy, expertise, services, training, and technical
+assistance to ensure the success of web application development projects.
+
+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://sensiolabs.com
+[3]: https://symfony.com/sponsor