use the external-dns slack channel, add section how to become a maint… (

#359)

* use the external-dns slack channel, add section how to become a maintainer for provider

* Update maintainer section

README.md

@@ -166,11 +166,25 @@ Have a look at [the milestones](https://github.com/kubernetes-incubator/external
 
 ## Contributing
 
-We encourage you to get involved with ExternalDNS, as users as well as contributors. Read the [contributing guidelines](CONTRIBUTING.md) and have a look at [the contributing docs](docs/contributing/getting-started.md) to learn about building the project, the project structure, and the purpose of each package.
+We encourage you to get involved with ExternalDNS, as users, contributors or as new maintainers that can take over some parts like different providers and help with code reviews.
 
-For an overview on how to write new Sources and Providers check out [Sources and Providers](docs/contributing/sources-and-providers.md).
+Providers which currently need maintainers:
+
+* Azure
+* Cloudflare
+* Digital Ocean
+* Google Cloud Platform
+
+Any provider should have at least one maintainer. It would be nice if you run it in production, but it is not required.
+You should check changes and make sure your provider is working correctly.
+
+It would be also great to have an automated end-to-end test for different cloud providers, so help from Kubernetes maintainers and their idea on how this can be done would be valuable.
 
-Feel free to reach out to us on the [Kubernetes slack](http://slack.k8s.io) in the #sig-network channel.
+Read the [contributing guidelines](CONTRIBUTING.md) and have a look at [the contributing docs](docs/contributing/getting-started.md) to learn about building the project, the project structure, and the purpose of each package.
+
+If you are interested please reach out to us on the [Kubernetes slack](http://slack.k8s.io) in the #external-dns channel.
+
+For an overview on how to write new Sources and Providers check out [Sources and Providers](docs/contributing/sources-and-providers.md).
 
 ## Heritage