Update ADOPTERS.md

ADOPTERS.md

@@ -3,3 +3,8 @@
 <!-- Add yourself here if you are using ESO in your company or your project! -->
 
 - [Pento](https://www.pento.io/)
+- [Mixpanel](https://mixpanel.com)
+- [K8S Website Infra](https://k8s.io/)
+
+
+Countless others that can't disclose that information! :)