docs(service_accounts): add non cluster-admin ex

docs/service_accounts.md

 # Tiller and Service Accounts
 
-In Kubernetes, granting a role to an application-specific service account is a best practice to ensure that your application is operating in the scope that you have specified. Read more about service account permissions in Kubernetes [here](https://kubernetes.io/docs/admin/authorization/rbac/#service-account-permissions).
+In Kubernetes, granting a role to an application-specific service account is a best practice to ensure that your application is operating in the scope that you have specified. Read more about service account permissions [in the official Kubernetes docs](https://kubernetes.io/docs/admin/authorization/rbac/#service-account-permissions). Bitnami also has a fantastic guide for [configuring RBAC in your cluster](https://docs.bitnami.com/kubernetes/how-to/configure-rbac-in-your-kubernetes-cluster/) that takes you through RBAC basics.
 
 You can add a service account to Tiller using the `--service-account <NAME>` flag while you're configuring helm. As a prerequisite, you'll have to create a role binding which specifies a [role](https://kubernetes.io/docs/admin/authorization/rbac/#role-and-clusterrole) and a [service account](https://kubernetes.io/docs/tasks/configure-pod-container/configure-service-account/) name that have been set up in advance.
 
 Once you have satisfied the pre-requisite and have a service account with the correct permissions, you'll run a command like this: `helm init --service-account <NAME>`
 
-## Example
+## Example: Service account with cluster-admin role
+
+```console
+$ kubectl create serviceaccount tiller --namespace kube-system
+```
 
 In `rbac-config.yaml`:
 ```yaml
 apiVersion: v1
 kind: ServiceAccount
 metadata:
-  name: helm
+  name: tiller
   namespace: kube-system
 ---
 apiVersion: rbac.authorization.k8s.io/v1beta1
 kind: ClusterRoleBinding
 metadata:
-  name: helm
+  name: tiller
 roleRef:
   apiGroup: rbac.authorization.k8s.io
   kind: ClusterRole
   name: cluster-admin
 subjects:
   - kind: ServiceAccount
-    name: helm
+    name: tiller
     namespace: kube-system
 ```
 
+_Note: The cluster-admin role is created by default in a Kubernetes cluster, so you don't have to define it explicitly._
 
 ```console
 $ kubectl create -f rbac-config.yaml
-$ helm init --service-account helm
+$ helm init --service-account tiller
+```
+
+## Example: Service account restricted to a namespace
+In the example above, we gave Tiller admin access to the entire cluster. You are not at all required to give Tiller cluster-admin access for it to work. Instead of specifying a ClusterRole or a ClusterRoleBinding, you can specify a Role and RoleBinding to limit Tiller's scope to a particular namespace.
+
+```console
+$ kubectl create namespace tiller-world
+namespace "tiller-world" created
+$ kubectl create serviceaccount tiller --namespace tiller-world
+serviceaccount "tiller" created
+```
+
+Define a Role like in `role-tiller.yaml`:
+```yaml
+kind: Role
+apiVersion: rbac.authorization.k8s.io/v1beta1
+metadata:
+  namespace: tiller-world
+  name: tiller-manager
+rules:
+- apiGroups: ["", "extensions", "apps"]
+  resources: ["deployments", "replicasets", "pods", "configmaps", "secrets", "namespaces"]
+  verbs: ["get", "list", "watch", "create", "update", "patch", "delete"] # You can also use ["*"]
+```
+
+```console
+$ kubectl create -f role-tiller.yaml
+role "tiller-manager" created
+```
+
+In `rolebinding-tiller.yaml`,
+```yaml
+kind: RoleBinding
+apiVersion: rbac.authorization.k8s.io/v1beta1
+metadata:
+  name: tiller-binding
+  namespace: tiller-world
+subjects:
+- kind: ServiceAccount
+  name: tiller
+  namespace: tiller-world
+roleRef:
+  kind: Role
+  name: tiller-manager
+  apiGroup: rbac.authorization.k8s.io
+```
+
+```console
+$ kubectl create -f rolebinding-tiller.yaml
+rolebinding "tiller-binding" created
+```
+
+```console
+$ helm init --service-account tiller --tiller-namespace tiller-world
+$HELM_HOME has been configured at /Users/awesome-user/.helm.
+
+Tiller (the helm server side component) has been installed into your Kubernetes Cluster.
+Happy Helming!
+
+$ helm install nginx --tiller-namespace tiller-world --namespace tiller-world
+NAME:   wayfaring-yak
+LAST DEPLOYED: Mon Aug  7 16:00:16 2017
+NAMESPACE: tiller-world
+STATUS: DEPLOYED
+
+RESOURCES:
+==> v1/Pod
+NAME                  READY  STATUS             RESTARTS  AGE
+wayfaring-yak-alpine  0/1    ContainerCreating  0         0s
 ```
 
-_Note: You do not have to specify a ClusterRole or a ClusterRoleBinding. You can specify a Role and RoleBinding instead to limit Tiller's scope to a particular namespace_