Update release notes, refs #23

Author: adangel

History.md

@@ -26,3 +26,4 @@
 *   [#19](https://github.com/pmd/pmd-regression-tester/pull/19): Add online mode for PmdTester - [BBG](https://github.com/djydewang)
 *   [#20](https://github.com/pmd/pmd-regression-tester/pull/20): Change the way of parsing xml file from DOM to SAX - [BBG](https://github.com/djydewang)
 *   [#21](https://github.com/pmd/pmd-regression-tester/pull/21): Add auto-gen-config option for PmdTester - [BBG](https://github.com/djydewang)
+*   [#23](https://github.com/pmd/pmd-regression-tester/pull/23): Preparing for the release of PmdTester - [BBG](https://github.com/djydewang)