[PPML] Add SGX plugin device readme (#5663)

* add sgx plugin device readme

ppml/trusted-big-data-ml/scala/docker-occlum/kubernetes/README.md

@@ -24,6 +24,7 @@ bash build-docker-image.sh
 2. Download [Spark 3.1.2](https://archive.apache.org/dist/spark/spark-3.1.2/spark-3.1.2-bin-hadoop2.7.tgz), and setup `SPARK_HOME`.
 3. `export kubernetes_master_url=your_k8s_master` or replace `${kubernetes_master_url}` with your k8s master url in `run_spark_xxx.sh`.
 4. Modify `driver.yaml` and `executor.yaml` for your applications.
+   In our demo example, we mount SGX devices into container or pod. Mount device requires privileged: true. In production deployment, please use K8S SGX device plugin with device-plugin setting in yaml.
 
 ## Examples
 

ppml/trusted-big-data-ml/scala/docker-occlum/kubernetes/driver.yaml

@@ -8,6 +8,8 @@ spec:
   - name: spark-example
     imagePullPolicy: Never
     volumeMounts:
+#    - name: device-plugin
+#      mountPath: /var/lib/kubelet/device-plugins
     - name: sgx-enclave
       mountPath: /dev/sgx/enclave
     - name: sgx-provision
@@ -30,6 +32,9 @@ spec:
     - name: SGX_KERNEL_HEAP
       value: "1GB"
   volumes:
+#    - name: device-plugin
+#      hostPath:
+#        path: /var/lib/kubelet/device-plugins
   - name: sgx-enclave
     hostPath:
       path: /dev/sgx_enclave

ppml/trusted-big-data-ml/scala/docker-occlum/kubernetes/executor.yaml

@@ -8,6 +8,8 @@ spec:
   - name: spark-example
     imagePullPolicy: Never
     volumeMounts:
+#    - name: device-plugin
+#      mountPath: /var/lib/kubelet/device-plugins
     - name: sgx-enclave
       mountPath: /dev/sgx/enclave
     - name: sgx-provision
@@ -30,6 +32,9 @@ spec:
     - name: SGX_KERNEL_HEAP
       value: "1GB"
   volumes:
+#    - name: device-plugin
+#      hostPath:
+#        path: /var/lib/kubelet/device-plugins
   - name: sgx-enclave
     hostPath:
       path: /dev/sgx_enclave