Looks ok but the following lines need to be addressed:
a1.channels.c1.kafka.producer.security.protocol = SASL_PLAINTEXT
+ a1.channels.c1.kafka.consumer.security.protocol = SASL_PLAINTEXT
s/c1/channel1 per the previous lines.
Also if we are going to take the time to document this does it make sense to include an example configuration with SASL_SSL as well? I see that it was called out in the change(i.e, look at the kafka docs) and that's probably fine. I could go either way really.