Readme describes the spr-cloud-dataflow-aggregate-task module

Section also discusses where to find tests
resolves spring-cloud#5446

spring-cloud-dataflow-aggregate-task/README.adoc

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+= Spring Cloud Dataflow Aggregate Task Module
+
+Spring Cloud Task and Spring Batch utilize a series of database tables to support storing data about Boot Application executions as well as Job executions.
+For each major release of these projects, their database schemas  adjust to meet the needs for the latest release.
+SCDF supports applications that may use the current release of these projects as well as a previous release.
+The `spring-cloud-dataflow-aggregate-task` module provides support for dataflow to query and mutate data in each of the schema versions.
+
+== Tests
+
+The tests for this module are located in the `spring-cloud-dataflow-server` module