Merge branch 'master' into fix_apiserver

Signed-off-by: Liyang Wang <liyang.wang@Ibm.com>

Author: Liyang Wang

README.md

@@ -4,6 +4,24 @@ Cert Manager's ACME (automated certificate management environment) issuer type s
 to implement custom DNS01 challenge solving logic.
 
 IBM Cloud Internet Services is not officially supported in cert-manager core, so if you want to automatically provision certificates with cert-manager using DNS challenges, you can use this repository to do so.
+=======
+This is useful if you need to use cert-manager with a DNS provider that is not
+officially supported in cert-manager core.
+
+## Why not in core?
+
+As the project & adoption has grown, there has been an influx of DNS provider
+pull requests to our core codebase. As this number has grown, the test matrix
+has become un-maintainable and so, it's not possible for us to certify that
+providers work to a sufficient level.
+
+By creating this 'interface' between cert-manager and DNS providers, we allow
+users to quickly iterate and test out new integrations, and then packaging
+those up themselves as 'extensions' to cert-manager.
+
+We can also then provide a standardised 'testing framework', or set of
+conformance tests, which allow us to validate that a DNS provider works as
+expected.
 
 ## Usage