[remkop#1342] Update RELEASE-NOTES for user manual 'Testing the Exit Code' improvement

Author: remkop

RELEASE-NOTES.md

@@ -42,6 +42,7 @@ Picocli follows [semantic versioning](http://semver.org/).
 * [#1323] DOC: Update Testing section of the user manual for Stefan Birkner's library [System-Lambda](https://github.com/stefanbirkner/system-lambda).
 * [#1325] DOC: Add section on Short and Long Option Columns to user manual. Thanks to [Andrei Ciobanu](https://github.com/nomemory) for raising this.
 * [#1336] DOC: Kotlin sample code, documentation improvements. Thanks to [Andreas Deininger](https://github.com/deining) for the pull request.
+* [#1342] DOC: Improve user manual chapter 28.3 'Testing the Exit Code'. Thanks to [Andreas Deininger](https://github.com/deining) for the pull request.
 * [#1313] DEP: Bump jline3Version in order to avoid stackoverflow error. Thanks to [Rupert Madden-Abbott](https://github.com/rupert-madden-abbott) for the pull request.
 * [#1336] BUILD: Bump Spring Boot, Gradle and Kotlin to latest version. Thanks to [Andreas Deininger](https://github.com/deining) for the pull request.
 * [#1327] BUILD: fix incorrect version in `MANIFEST.MF`. Thanks to [Fiouz](https://github.com/Fiouz) for the pull request.