Update README for v0.6 release

Author: Florian Eckerstorfer

README.md

@@ -76,6 +76,10 @@ In practice, the following methods will throw an exception if called on a Window
 Change Log
 ----------
 
+### Version 0.6 (10 July 2016)
+
+- [#17](https://github.com/cocur/background-process/pull/17) Add ability to append to file on Unix/Linux-based systems (by [bpolaszek](https://github.com/bpolaszek))
+
 ### Version 0.5 (24 October 2015)
 
 - Added basic support for Windows