Add DCO to README

Author: Dave Syer

README.md

@@ -155,7 +155,8 @@ Here is a list of them:
 
 The [issue tracker](https://github.com/spring-projects/spring-petclinic/issues) is the preferred channel for bug reports, feature requests and submitting pull requests.
 
-For pull requests, editor preferences are available in the [editor config](.editorconfig) for easy use in common text editors. Read more and download plugins at <https://editorconfig.org>. If you have not previously done so, please fill out and submit the [Contributor License Agreement](https://cla.pivotal.io/sign/spring).
+For pull requests, editor preferences are available in the [editor config](.editorconfig) for easy use in common text editors. Read more and download plugins at <https://editorconfig.org>. All commits must include a __Signed-off-by__ trailer at the end of each commit message to indicate that the contributor agrees to the Developer Certificate of Origin.
+For additional details, please refer to the blog post [Hello DCO, Goodbye CLA: Simplifying Contributions to Spring](https://spring.io/blog/2025/01/06/hello-dco-goodbye-cla-simplifying-contributions-to-spring).
 
 ## License