[Website] update content of community case study page (#25023)

website/www/site/content/en/community/case-study.md

@@ -25,10 +25,7 @@ Your company uses Apache Beam? There are several options to highlight it and mak
 
 ## Share your story
 
-Sharing your story and making a Case Study out of it might have a significant impact on helping users with adopting
-Apache Beam. And, of course, gaining interest for your company.
-<a href="mailto:dev@beam.apache.org?subject=Beam Website Add New Case Stud">Contact the community</a> to get Case Study
-started!
+Sharing your story and making a Case Study out of it might have a significant impact on helping users with adopting Apache Beam. And, of course, gaining interest for your company. Please see [how to add a new case study](https://github.com/apache/beam/blob/master/website/ADD_CASE_STUDY.md) for the next steps, templates and helpful tips. If you have any questions about adding a case study, please [contact the community](mailto:dev@beam.apache.org?subject=Beam%20Website%20Add%20New%20Case%20Study).
 
 ## Add your logo