Add RBAC documentation for Runner

doc/install/kubernetes/gitlab_runner_chart.md

@@ -72,6 +72,18 @@ concurrent: 10
 ##
 checkInterval: 30
+## For RBAC support:
+rbac:
+  create: false
+
+  ## Run the gitlab-bastion container with the ability to deploy/manage containers of jobs
+  ## cluster-wide or only within namespace
+  clusterWideAccess: false
+
+  ## Use the following Kubernetes Service Account name if RBAC is disabled in this Helm chart (see rbac.create)
+  ##
+  # serviceAccountName: default
+
 ## Configuration for the Pods that that the runner launches for each new job
 ##
 runners:
@@ -116,6 +128,12 @@ runners:
 ```
+### Enabling RBAC support
+
+If your cluster has RBAC enabled, you can choose to either have the chart create its own sevice account or provide one.
+
+To have the chart create the service account for you, set `rbac.create` to true. 
+
 ### Controlling maximum Runner concurrency
 A single GitLab Runner deployed on Kubernetes is able to execute multiple jobs in parallel by automatically starting additional Runner pods. The [`concurrent` setting](https://docs.gitlab.com/runner/configuration/advanced-configuration.html#the-global-section) controls the maximum number of pods allowed at a single time, and defaults to `10`.