chore(docs): add kubernetes compatibility matrix (#19)

Signed-off-by: Cyril Corbon <corboncyril@gmail.com>

README.md

@@ -14,12 +14,14 @@
 - Join Kubernetes slack and join [druid-operator](https://kubernetes.slack.com/archives/C04F4M6HT2L)
 
 ### Talks and Blogs on Druid Operator
+
 - [Dok Community](https://www.youtube.com/live/X4A3lWJRGHk?feature=share)
 - [Druid Summit](https://youtu.be/UqPrttXRBDg)
 - [Druid Operator Blog](https://www.cloudnatively.com/apache-druid-on-kubernetes/)
 - [Druid On K8s Without ZK](https://youtu.be/TRYOvkz5Wuw)
 
 ### Supported CR
+
 - The operator supports CR of type ```Druid```.
 - ```Druid``` CR belongs to api Group ```druid.apache.org``` and version ```v1alpha1```
 
@@ -28,13 +30,23 @@
 ![Druid Operator](docs/images/druid-operator.png?raw=true "Druid Operator")
 
 ### Notifications
+
 - Users may experience HPA issues with druid-operator with release 0.0.5, as described in the [issue](https://github.com/druid-io/druid-operator/issues/160).
 - The latest release 0.0.6 has fixes for the above issue.
 - The operator has moved from HPA apiVersion autoscaling/v2beta1 to autoscaling/v2beta2 API users will need to update there HPA Specs according v2beta2 api in order to work with the latest druid-operator release.
 - Users may experience pvc deletion [issue](https://github.com/druid-io/druid-operator/issues/186) in release 0.0.6, this issue has been fixed in patch release 0.0.6.1.
 - druid-operator has moved Ingress apiVersion networking/v1beta1 to networking/v1. Users will need to update there Ingress Spec in the druid CR according networking/v1 syntax. In case users are using schema validated CRD, the CRD will also be needed to be updated.
 - druid-operator has moved PodDisruptionBudget apiVersion policy/v1beta1 to policy/v1. Users will need to update there Kubernetes versions to 1.21+ to use druid-operator tag 0.0.9+.
-- The latest release for druid-operator is v1.0.0, this release is compatible with k8s version 1.25. HPA API is kept to version v2beta2. 
+- The latest release for druid-operator is v1.0.0, this release is compatible with k8s version 1.25. HPA API is kept to version v2beta2.
+
+### Kubernetes version compatibility
+
+| druid-operator | 0.0.9 | v1.0.0 |
+| :------------- | :-------------: | :-----: |
+| kubernetes <= 1.20 | :x:| :x: |
+| kubernetes == 1.21 | :white_check_mark:| :x: |
+| kubernetes >= 1.22 and < 1.25 | :white_check_mark: | :white_check_mark: |
+| kubernetes > 1.25 | :x: | :white_check_mark: |
 
 ### Contributors