GH-2139: Clarify ExponentialBackOff maxDelay default

The wording in `@BackOff`'s maxDelay property's javadoc is a bit ambiguous. Clarify its default behavior in the Retryable Topic's documentation.

Author: tomazfernandes

Diff for: spring-kafka-docs/src/main/asciidoc/index.adoc

@@ -5,7 +5,7 @@
 :numbered:
 :icons: font
 :hide-uri-scheme:
-Gary Russell; Artem Bilan; Biju Kunjummen; Jay Bryant; Soby Chacko
+Gary Russell; Artem Bilan; Biju Kunjummen; Jay Bryant; Soby Chacko; Tomaz Fernandes
 
 ifdef::backend-html5[]
 *{project-version}*

Diff for: spring-kafka-docs/src/main/asciidoc/retrytopic.adoc

@@ -189,7 +189,7 @@ public RetryTopicConfiguration myRetryTopic(KafkaTemplate<String, MyPojo> templa
 ----
 ====
 
-You can also provide a custom implementation of Spring Retry's `SleepingBackOffPolicy`:
+You can also provide a custom implementation of Spring Retry's `SleepingBackOffPolicy` interface:
 
 ====
 [source, java]
@@ -205,9 +205,12 @@ public RetryTopicConfiguration myRetryTopic(KafkaTemplate<String, MyPojo> templa
 ----
 ====
 
-NOTE: The default backoff policy is FixedBackOffPolicy with a maximum of 3 attempts and 1000ms intervals.
+NOTE: The default backoff policy is `FixedBackOffPolicy` with a maximum of 3 attempts and 1000ms intervals.
 
-IMPORTANT: The first attempt counts against the maxAttempts, so if you provide a maxAttempts value of 4 there'll be the original attempt plus 3 retries.
+NOTE: There is a 30-second default maximum delay for the `ExponentialBackOffPolicy`.
+If your back off policy requires delays with values bigger than that, adjust the maxDelay property accordingly.
+
+IMPORTANT: The first attempt counts against `maxAttempts`, so if you provide a `maxAttempts` value of 4 there'll be the original attempt plus 3 retries.
 
 ===== Single Topic Fixed Delay Retries