chore: regenerate README (#220)

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<details><summary>Log from Synthtool</summary>

```
2021-07-27 23:31:54,702 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-pubsublite-spark/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-07-27 23:31:56,146 synthtool [DEBUG] > Wrote metadata to .github/readme/synth.metadata/synth.metadata.

```
</details>

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.github/readme/synth.metadata/synth.metadata

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-pubsublite-spark.git",
-        "sha": "f7e3707d11096e749665019beff0cd90db829651"
+        "sha": "d39175b2d0a642186933696734ee16867cb67e76"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "387851d0e88ca4a5b1771ad63d915bed1bd4a740"
+        "sha": "3d32990b6f4b57be77455e3ca89e6e21cd0c06b3"
       }
     }
   ]

README.md

@@ -11,11 +11,13 @@ Java idiomatic client for [Pub/Sub Lite Spark Connector][product-docs].
 > Note: This client is a work-in-progress, and may occasionally
 > make backwards-incompatible changes.
 
+
 ## Quickstart
 
 
 If you are using Maven, add this to your pom.xml file:
 
+
 ```xml
 <dependency>
   <groupId>com.google.cloud</groupId>
@@ -25,11 +27,13 @@ If you are using Maven, add this to your pom.xml file:
 ```
 
 If you are using Gradle without BOM, add this to your dependencies
+
 ```Groovy
 compile 'com.google.cloud:pubsublite-spark-sql-streaming:0.3.0'
 ```
 
 If you are using SBT, add this to your dependencies
+
 ```Scala
 libraryDependencies += "com.google.cloud" % "pubsublite-spark-sql-streaming" % "0.3.0"
 ```
@@ -38,6 +42,10 @@ libraryDependencies += "com.google.cloud" % "pubsublite-spark-sql-streaming" % "
 
 See the [Authentication][authentication] section in the base directory's README.
 
+## Authorization
+
+The client application making API calls must be granted [authorization scopes][auth-scopes] required for the desired Pub/Sub Lite Spark Connector APIs, and the authenticated principal must have the [IAM role(s)][predefined-iam-roles] required to access GCP resources using the Pub/Sub Lite Spark Connector API calls.
+
 ## Getting Started
 
 ### Prerequisites
@@ -223,8 +231,7 @@ Example:
 
 ## Samples
 
-Samples are in the [`samples/`](https://github.com/googleapis/java-pubsublite-spark/tree/master/samples) directory. The samples' `README.md`
-has instructions for running the samples.
+Samples are in the [`samples/`](https://github.com/googleapis/java-pubsublite-spark/tree/master/samples) directory.
 
 | Sample                      | Source Code                       | Try it |
 | --------------------------- | --------------------------------- | ------ |
@@ -299,6 +306,7 @@ This library follows [Semantic Versioning](http://semver.org/).
 It is currently in major version zero (``0.y.z``), which means that anything may change at any time
 and the public API should not be considered stable.
 
+
 ## Contributing
 
 
@@ -310,6 +318,7 @@ Please note that this project is released with a Contributor Code of Conduct. By
 this project you agree to abide by its terms. See [Code of Conduct][code-of-conduct] for more
 information.
 
+
 ## License
 
 Apache 2.0 - See [LICENSE][license] for more information.
@@ -341,6 +350,9 @@ Java is a registered trademark of Oracle and/or its affiliates.
 [maven-version-image]: https://img.shields.io/maven-central/v/com.google.cloud/pubsublite-spark-sql-streaming.svg
 [maven-version-link]: https://search.maven.org/search?q=g:com.google.cloud%20AND%20a:pubsublite-spark-sql-streaming&core=gav
 [authentication]: https://github.com/googleapis/google-cloud-java#authentication
+[auth-scopes]: https://developers.google.com/identity/protocols/oauth2/scopes
+[predefined-iam-roles]: https://cloud.google.com/iam/docs/understanding-roles#predefined_roles
+[iam-policy]: https://cloud.google.com/iam/docs/overview#cloud-iam-policy
 [developer-console]: https://console.developers.google.com/
 [create-project]: https://cloud.google.com/resource-manager/docs/creating-managing-projects
 [cloud-sdk]: https://cloud.google.com/sdk/