docs: improve PubsubLiteIO readme (#586)

Author: anguillanneuf

pubsublite-beam-io/README.md

@@ -1,28 +1,32 @@
 # Instructions for PubsubLiteIO usage.
 
-NOTE: Drain is not currently supported on PubsubLiteIO. Once Beam 2.29.0 is released, this will be supported
-only when --experiments=use_runner_v2 is enabled. Please contact dataflow customer support to request adding projects
-into the allowlist and launch the pipeline with --experiments=use_runner_v2.
+NOTE: Drain is not currently supported on `PubsubLiteIO`. Once Beam 2.29.0 is released, this will be supported
+only when `--experiments=use_runner_v2` is enabled. Please contact dataflow customer support to request adding projects
+into the allowlist and launch the pipeline with `--experiments=use_runner_v2`.
 
-1. Add the following to your POM file to download the Pub/Sub Lite I/O.
+1. Add the following to your `pom.xml` file to download the Pub/Sub Lite I/O.
 ```xml
 <dependency>
-   <groupId>com.google.cloud.pubsublite</groupId>
+   <groupId>com.google.cloud</groupId>
    <artifactId>pubsublite-beam-io</artifactId>
-   <version>0.11.0</version>
+   <version>0.13.1</version>
 </dependency>
 ```
-1. Create a topic using `gcloud pubsub lite-topics create`
+1. Create a topic using [`gcloud pubsub lite-topics create`](https://cloud.google.com/sdk/gcloud/reference/pubsub/lite-topics/create)
 1. Write some messages using:
 
     ```java
     import com.google.cloud.pubsublite.beam.PubsubLiteIO;
     import com.google.cloud.pubsublite.beam.PublisherOptions;
     import com.google.cloud.pubsublite.proto.PubSubMessage;
+    import com.google.cloud.pubsublite.CloudZone;
+    import com.google.cloud.pubsublite.ProjectIdOrNumber;
+    import com.google.cloud.pubsublite.TopicName;
+    import com.google.cloud.pubsublite.TopicPath;
 
     ...
 
-    private final static String ZONE = "us-central1-b";
+    private final static String LOCATION = "us-central1-b";
     private final static Long PROJECT_NUM = 123L;
 
     ...
@@ -32,23 +36,26 @@ into the allowlist and launch the pipeline with --experiments=use_runner_v2.
         PublisherOptions.newBuilder()
             .setTopicPath(TopicPath.newBuilder()
                 .setLocation(CloudZone.parse(ZONE))
-                .setProject(ProjectNumber.of(PROJECT_NUM))
+                .setProject(ProjectIdOrNumber.of(PROJECT_NUM))
                 .setName(TopicName.of("my-topic"))
                 .build())
             .build()));
     ```
-1. Create a subscription using `gcloud pubsub lite-subscriptions create`
+1. Create a subscription using [`gcloud pubsub lite-subscriptions create`](https://cloud.google.com/sdk/gcloud/reference/pubsub/subscriptions/create)
 1. Read some messages using:
 
     ```java
     import com.google.cloud.pubsublite.beam.PubsubLiteIO;
     import com.google.cloud.pubsublite.beam.SubscriberOptions;
     import com.google.cloud.pubsublite.proto.SequencedMessage;
-    import com.google.cloud.pubsublite.*;
+    import com.google.cloud.pubsublite.CloudZone;
+    import com.google.cloud.pubsublite.ProjectIdOrNumber;
+    import com.google.cloud.pubsublite.SubscriptionName;
+    import com.google.cloud.pubsublite.SubscriptionPath;
 
     ...
 
-    private final static String ZONE = "us-central1-b";
+    private final static String LOCATION = "us-central1-b";
     private final static Long PROJECT_NUM = 123L;
 
     ...
@@ -57,9 +64,24 @@ into the allowlist and launch the pipeline with --experiments=use_runner_v2.
     PCollection<SequencedMessage> messages = pipeline.apply("Read messages", PubsubLiteIO.read(
         SubscriberOptions.newBuilder()
             .setSubscriptionPath(SubscriptionPath.newBuilder()
-                .setLocation(CloudZone.parse(ZONE))
-                .setProject(ProjectNumber.of(PROJECT_NUM))
+                .setLocation(CloudZone.parse(LOCATION))
+                .setProject(ProjectIdOrNumber.of(PROJECT_NUM))
                 .setName(SubscriptionName.of("my-sub"))
                 .build())
             .build()));
     ```
+
+### Known issues and workarounds
+1. If you encounter `IllegalAccessError` as shown below, place the Pub/Sub Lite
+ I/O connector as the first dependency before all other Beam dependencies in
+  your `pom.xml`.
+
+    >`java.lang.IllegalAccessError: failed to access class com.google.cloud.
+    pubsublite.internal.wire.RoutingMetadata from class com.google.cloud.
+    pubsublite.beam.SubscriberOptions (com.google.cloud.pubsublite.internal.
+    wire.RoutingMetadata and com.google.cloud.pubsublite.beam.SubscriberOptions
+    are in unnamed module of loader java.net.URLClassLoader @ff2266c)`
+
+1. Aggregate transforms after fixed windowing will not emit elements in the
+DirectRunner for Pub/Sub Lite I/O unless you explicitly fire after watermark
+triggers, or use processing-time triggers instead.