docs: additional explanation about schema in README

Signed-off-by: Dale Lane <dale.lane@uk.ibm.com>

Author: dalelane

README.md

@@ -312,7 +312,7 @@ The configuration options for the Kafka Connect source connector for IBM MQ are
 | `mq.receive.max.poll.time.ms`                   | Maximum time (in milliseconds) to poll messages in a single Kafka Connect task cycle. If set to 0, polling continues until batch size or a receive returns null.        | long    | 0              | 0 or greater                                                                                                                                                                        |
 | `errors.deadletterqueue.topic.name`             | The name of the Kafka topic to use as the dead letter queue (DLQ) for poison messages that fail during processing within the record builder component of the connector. | string  |                | If left blank (default), failed messages will not be written to a DLQ.                                                                                                              |
 | `errors.deadletterqueue.context.headers.enable` | Whether to add error context headers to messages written to the DLQ.                                                                                                    | boolean | false          | When enabled, additional headers describing the error will be included with each DLQ record.                                                                                        |
-| `mq.record.builder.json.schemas.enable`         | (JSON record builder only) Include schemas within Kafka messages. This is used as the `schemas.enable` config for the JsonConverter used by the JSON record builder     | boolean | false          |                                                                                                                                                                                     |
+| `mq.record.builder.json.schemas.enable`         | (JSON record builder only) Include schemas within Kafka messages. This is used as the `schemas.enable` config for the JsonConverter used by the JSON record builder. If true, a schema must be provided - either using `mq.record.builder.json.schema.content` or by embedding a schema within each MQ message payload. | boolean | false          |                                                                                                                                                                                     |
 | `mq.record.builder.json.schema.content`         | (JSON record builder only) Schema to use for all messages. This is used as the `schema.content` config for the JsonConverter used by the JSON record builder.           | string  |                | This should be a Kafka Connect schema, as used by JsonConverter.                                                                                                                    |
 
 ### Using a CCDT file