docs: document shell completion feature (argoproj#1509)

Signed-off-by: Kostis Kapelonis <[email protected]>

Author: kostis-codefresh

docs/installation.md

@@ -65,6 +65,17 @@ Test to ensure the version you installed is up-to-date:
 kubectl argo rollouts version
 ```
 
+## Shell auto completion
+
+The CLI can export shell completion code for several shells.
+
+For bash, ensure you have bash completions installed and enabled. To access completions in your current shell, run $ `source <(kubectl-argo-rollouts completion bash)`. Alternatively, write it to a file and source in `.bash_profile`.
+
+The completion command supports bash, zsh, fish and powershell.
+
+See the [completion command documentation](./generated/kubectl-argo-rollouts/kubectl-argo-rollouts_completion.md) for more details.
+
+
 ## Using the CLI  with Docker
 
 The CLI is also available as a container image at [https://quay.io/repository/argoproj/kubectl-argo-rollouts](https://quay.io/repository/argoproj/kubectl-argo-rollouts)