Add note on async invocations for the Kafka connector

Signed-off-by: Han Verstraete (OpenFaaS Ltd) <[email protected]>

Author: welteki

docs/openfaas-pro/kafka-events.md

@@ -103,6 +103,14 @@ The queue-worker has a set of default retry values set via the Helm chart. They
 * [Quick start with the Helm chart - self-hosted, SASL and TLS Client Certificates](https://github.com/openfaas/faas-netes/blob/master/chart/kafka-connector/quickstart.md)
 * Original launch blog post: [Staying on topic: trigger your OpenFaaS functions with Apache Kafka](https://www.openfaas.com/blog/kafka-connector/)
 
+## Async invocations
+
+The connector can be configured to invoke function asynchronously. This lets you use [OpenFaaS async](https://docs.openfaas.com/reference/async/) features like retries.
+
+To prevent the connector from consuming all Kafka messages at once and submitting them to the OpenFaaS async queue a limit on the number of inflight async invocations can be configured.
+
+See the [Kafka connector README](https://github.com/openfaas/faas-netes/blob/master/chart/kafka-connector/README.md#async-invocations) to configure the connector for async invocations.
+
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