Add kubernetes site option documentation. (#5920)

docs/site-aliases.md

@@ -127,6 +127,10 @@ is really nothing more than a collection of options.
     - **service**: the name of the container to run on.
     - **exec**:
         - **options**: Options for the exec subcommand.
+- **kubectl** When specified, Drush executes via `kubectl` exec rather than `ssh`.
+    - **namespace** The namespace to execute the command in.
+    - **resource** The k8s object to execute the command on.
+    - **container** The container in the resource to execute the command on.
 - **os**: The operating system of the remote server.  Valid values
   are _Windows_ and _Linux_. Set this value for all remote
   aliases where the remote's OS differs from the local. This is especially relevant
@@ -233,7 +237,7 @@ does not exist (e.g. if the user made a typo). An alias alter hook in a
 policy file may be used to catch these mistakes and report an error.
 See [SiteAliasAlterCommands](https://www.drush.org/latest/examples/SiteAliasAlterCommands.php/) for an example on how to do this.
 
-### Docker Compose and other transports
+### Docker Compose
 
 The example below shows drush calling into a Docker hosted site. See the https://github.com/consolidation/site-alias and https://github.com/consolidation/site-process projects for more developer
 information about transports. 
@@ -267,6 +271,26 @@ dev:
   uri: https://dev.example.com
 ```
 
+### Kubernetes
+
+Drush provides transport for running drush commands on your Kubernetes cluster via [kubectl](https://kubernetes.io/docs/reference/kubectl/). See an example and options below.
+
+ ```yml
+ prod: 
+   kubectl:
+     namespace: 'my-drupal-namespace'
+     resource: 'pods/my-drupal-pod' 
+     container: 'drupal'
+ ```
+
+#### Key options
+  * **namespace:** The namespace where your Drupal deployment resides.
+  * **resource:**  Kubernetes resource type (usually 'pods').
+  * **container:** The specific container within the pod where Drupal runs.
+  * **kubeconfig:** The kubeconfig file to use for authentication.
+  * **entrypoint:** The command to use as the container entrypoint.
+
+
 ### Example of rsync with exclude-paths
 
 Note that most options typically passed to rsync via `drush rsync` are