Add changelog for splitting off log4j-async-logger

Author: ppkarwasz

src/changelog/.3.x.x/create_async_logger.xml

@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xmlns="http://logging.apache.org/log4j/changelog"
+       xsi:schemaLocation="http://logging.apache.org/log4j/changelog https://logging.apache.org/log4j/changelog-0.1.2.xsd"
+       type="changed">
+  <description format="asciidoc">
+    Split off async logger support into a new `log4j-async-logger` module.
+  </description>
+</entry>