Add sponsors for 5.3

Author: fabpot

README.md

@@ -41,6 +41,17 @@ $url = $generator->generate('blog_show', [
 // $url = '/blog/my-blog-post'
 ```
 
+Sponsor
+-------
+
+The Routing component for Symfony 5.3 is [backed][1] by [redirection.io][2].
+
+redirection.io logs all your website’s HTTP traffic, and lets you fix errors
+with redirect rules in seconds. Give your marketing, SEO and IT teams the right
+tool to manage your website traffic efficiently! 
+
+Help Symfony by [sponsoring][3] its development!
+
 Resources
 ---------
 
@@ -49,3 +60,7 @@ 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://redirection.io/
+[3]: https://symfony.com/sponsor