Polish "Add support for configuring Liquibase tag property"

See gh-19316

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/liquibase/LiquibaseAutoConfiguration.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2020 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/liquibase/LiquibaseProperties.java

@@ -116,7 +116,9 @@ public class LiquibaseProperties {
 	private boolean testRollbackOnUpdate;
 
 	/**
-	 * Name of the tag.
+	 * Tag name to use when applying database changes. Can also be used with
+	 * "rollbackFile" to generate a rollback script for all existing changes associated
+	 * with that tag.
 	 */
 	private String tag;