Update docs. (awspring#644)

Author: maciejwalkowiak

docs/src/main/asciidoc/_configprops.adoc

@@ -61,7 +61,7 @@
 |spring.cloud.aws.sns.region |  | Overrides the default region.
 |spring.cloud.aws.sqs.enabled | `+++true+++` | Enables SQS integration.
 |spring.cloud.aws.sqs.endpoint |  | Overrides the default endpoint.
-|spring.cloud.aws.sqs.listener.max-inflight-messages-per-queue |  | The maximum number of simultaneous inflight messages in a queue.
+|spring.cloud.aws.sqs.listener.max-concurrent-messages |  | The maximum concurrent messages that can be processed simultaneously for each queue. Note that if acknowledgement batching is being used, the actual maximum number of messages inflight might be higher.
 |spring.cloud.aws.sqs.listener.max-messages-per-poll |  | The maximum number of messages to be retrieved in a single poll to SQS.
 |spring.cloud.aws.sqs.listener.poll-timeout |  | The maximum amount of time for a poll to SQS.
 |spring.cloud.aws.sqs.region |  | Overrides the default region.

docs/src/main/asciidoc/migration.adoc

@@ -1,5 +1,10 @@
 == Migration from 2.x to 3.x
 
+[WARNING]
+====
+Migration guide is work in progress.
+====
+
 Properties that have changed from 2.x to 3.x are listed below:
 
 [cols="2*", options="header", width=100%, %autowidth]