Add adopters file (#506)

Signed-off-by: Anders Eknert <anders@styra.com>

README.md

@@ -44,6 +44,8 @@ with linting.
 
 — Shawn McGuire, [Atlassian](https://www.atlassian.com/)
 
+See the [adopters](/docs/adopters.md) file for more Regal users.
+
 ## Getting Started
 
 ### Download Regal

docs/adopters.md

@@ -0,0 +1,44 @@
+# Adopters
+
+We're happy to be trusted by the following projects and organizations.
+
+If you're using Regal, please consider opening a pull request to add your project or organization to this list!
+
+## Open Source Projects
+
+Public open source projects integrating Regal for linting in their CI/CD pipelines.
+
+- [Brainiac](https://github.com/carbonetes/brainiac)
+- [Cloudbeat](https://github.com/elastic/cloudbeat)
+- [Conftest](https://github.com/open-policy-agent/conftest)
+- [CVAT](https://github.com/opencv/cvat)
+- [GKE Policy Automation](https://github.com/google/gke-policy-automation)
+- [Konstraint](https://github.com/plexsystems/konstraint)
+- [Kubescape](https://github.com/kubescape/regolibrary)
+- [Legitify](https://github.com/Legit-Labs/legitify)
+- [Modernisation Platform](https://github.com/ministryofjustice/modernisation-platform)
+- [OPA Library](https://github.com/open-policy-agent/library)
+- [Red Hat COP](https://github.com/redhat-cop/rego-policies)
+- [ScubaGear](https://github.com/cisagov/ScubaGear)
+- [Spacelift Policy Library](https://github.com/spacelift-io/spacelift-policies-example-library)
+
+## Integrations
+
+Projects and products that integrate Regal into their offerings.
+
+- [Dependency Management Data](https://gitlab.com/tanna.dev/dependency-management-data)
+- [Enterprise OPA](https://github.com/styrainc/enterprise-opa)
+
+## Companies and Organizations
+
+Companies and organizations using Regal (not counting organizations behind the open source projects listed above).
+
+- [Atlassian](https://www.atlassian.com)
+- [Bankdata](https://www.bankdata.dk)
+- [Miro](https://miro.com)
+- [Styra](https://www.styra.com)
+
+## Community
+
+If you'd like to discuss Regal adoption or just talk about Regal in general, please join us in the `#regal`
+channel in the Styra Community [Slack](https://communityinviter.com/apps/styracommunity/signup)!