doc: Add sample common issues.

.readme-partials.yaml

@@ -19,13 +19,10 @@ custom_content: |
   <!--- TODO(jiangmichael): Release on Maven Central and add Maven Central link -->
     The connector will be available from the Maven Central repository. It can be used using the `--packages` option or the `spark.jars.packages` configuration property.
 
-  <!--
-    | Scala version | Connector Artifact |
-    | --- | --- |
-    | Scala 2.11 | `com.google.cloud.pubsublite.spark:pubsublite-spark-sql-streaming:0.1.0:with-dependencies` |
-  -->
-
-  <!--- TODO(jiangmichael): Add exmaple code and brief description here -->
+  ## Compatibility
+  | Connector version | Spark version |
+  | --- | --- |
+  | 0.1.0 | 2.4.X |
 
   ## Usage
 

samples/README.md

@@ -87,4 +87,14 @@ To run the word count sample in Dataproc cluster, follow the steps:
 3. Delete Dataproc cluster.
    ```sh
    gcloud dataproc clusters delete $CLUSTER_NAME --region=$REGION
-   ```
+   ```
+
+## Common issues
+1. Permission not granted. <br>
+   This could happen when creating topic and subscription, or submitting a job to your Dataproc cluster.
+   Make sure your service account has at least `Editor` permissions for Pub/Sub Lite and Dataproc. 
+   Your Dataproc cluster needs `scope=cloud-platform` to access other services and resources within the same project.
+   Your `gcloud` and `GOOGLE_APPLICATION_CREDENTIALS` should access the same project. Check out which project your `gcloud` and `gstuil` commands use with `gcloud config get-value project`.
+
+2. Your Dataproc job fails with `ClassNotFound` or similar exceptions. <br>
+   Make sure your Dataproc cluster uses images of [supported Spark versions](https://github.com/googleapis/java-pubsublite-spark#compatibility).