use stringData in secret yaml to store huggingface token (#25685)

Signed-off-by: yiting.jiang <yiting.jiang@daocloud.io>

docs/deployment/k8s.md

@@ -49,11 +49,14 @@ First, create a Kubernetes PVC and Secret for downloading and storing Hugging Fa
     metadata:
       name: hf-token-secret
     type: Opaque
-    data:
-      token: $(HF_TOKEN)
+    stringData:
+      token: "REPLACE_WITH_TOKEN"
     EOF
     ```
 
+Here, the `token` field stores your **Hugging Face access token**. For details on how to generate a token,
+see the [Hugging Face documentation](https://huggingface.co/docs/hub/en/security-tokens).
+
 Next, start the vLLM server as a Kubernetes Deployment and Service:
 
 ??? console "Config"