docs(kafka_bridge): minor fixes to license and readme

Fixes https://emqx.atlassian.net/browse/EMQX-9481

LICENSE

@@ -4,4 +4,8 @@ For EMQX: Apache License 2.0, see APL.txt,
 which applies to all source files except for lib-ee sub-directory.
 
 For EMQX Enterprise (since version 5.0): Business Source License 1.1,
-see lib-ee/BSL.txt, which applies to source code in lib-ee sub-directory.
+see lib-ee/BSL.txt, which applies to source code in lib-ee
+sub-directory and some of the apps under the apps directory.
+
+Source code under apps that uses BSL License:
+- apps/emqx_bridge_kafka

apps/emqx_bridge_kafka/README.md

@@ -10,10 +10,21 @@ workers from `emqx_resource`.  It implements the connection management
 and interaction without need for a separate connector app, since it's
 not used by authentication and authorization applications.
 
-## Contributing
+# Documentation links
+
+For more information on Apache Kafka, please see its [official
+site](https://kafka.apache.org/).
+
+# Configurations
+
+Please see [our official
+documentation](https://www.emqx.io/docs/en/v5.0/data-integration/data-bridge-kafka.html)
+for more detailed info.
+
+# Contributing
 
 Please see our [contributing.md](../../CONTRIBUTING.md).
 
-## License
+# License
 
 See [BSL](./BSL.txt).