docs: alternative installation method (#110)

Signed-off-by: Kostis Kapelonis <kostis@codefresh.io>

Author: kostis-codefresh

docs/installation.md

@@ -11,15 +11,15 @@ Follow the [official instructions](https://argo-rollouts.readthedocs.io/en/stabl
 
 Optionally install the [Argo Rollouts CLI](https://argoproj.github.io/argo-rollouts/features/kubectl-plugin/) in order to control Rollouts from your terminal.
 
-## Installing the plugin
+## Installing the plugin via HTTP(S)
 
 To install the plugin create a configmap with the following syntax:
 
 ```yaml
 apiVersion: v1
 kind: ConfigMap
 metadata:
-  name: argo-rollouts-config # must be so name
+  name: argo-rollouts-config # must be named like this
   namespace: argo-rollouts # must be in this namespace
 data:
   trafficRouterPlugins: |-
@@ -35,7 +35,7 @@ For example for a Linux/x86 cluster save the following in a file of your choosin
 apiVersion: v1
 kind: ConfigMap
 metadata:
-  name: argo-rollouts-config # must be so name
+  name: argo-rollouts-config # must be named like this
   namespace: argo-rollouts # must be in this namespace
 data:
   trafficRouterPlugins: |-
@@ -45,6 +45,35 @@ data:
 
 Deploy this file with `kubectl apply -f gateway-plugin.yml -n argo-rollouts`. You can also use [Argo CD](https://argoproj.github.io/cd/) or any other Kubernetes deployment method that you prefer.
 
+## Installing the plugin via init containers
+
+Use the [Argo Rollouts Helm chart](https://argoproj.github.io/argo-helm/) and change the [default values](https://artifacthub.io/packages/helm/argo/argo-rollouts):
+
+```yaml
+controller:
+    initContainers:                                   
+      - name: copy-gwapi-plugin
+        image: ghcr.io/argoproj-labs/rollouts-plugin-trafficrouter-gatewayapi:v0.5.0
+        command: ["/bin/sh", "-c"]                    
+        args:
+          - cp /bin/rollouts-plugin-trafficrouter-gatewayapi /plugins
+        volumeMounts:                                 
+          - name: gwapi-plugin
+            mountPath: /plugins
+    trafficRouterPlugins:                             
+      trafficRouterPlugins: |-
+        - name: argoproj-labs/gatewayAPI
+          location: "file:///plugins/rollouts-plugin-trafficrouter-gatewayapi"  
+    volumes:                                           
+      - name: gwapi-plugin
+        emptyDir: {}
+    volumeMounts:                                      
+      - name: gwapi-plugin
+        mountPath: /plugins
+```        
+
+We publish [container images](https://github.com/argoproj-labs/rollouts-plugin-trafficrouter-gatewayapi/pkgs/container/rollouts-plugin-trafficrouter-gatewayapi) for both ARM and x86.
+
 For more installation options see the [Plugin documentation](https://argoproj.github.io/argo-rollouts/features/traffic-management/plugins/) at the main Argo Rollouts site.
 
 ## Verifying the installation