Add on what OS the build test is run.

GerryFerdinandus · GerryFerdinandus · commit d377d2b3765d · 2016-02-13T16:18:04.000+01:00
diff --git a/README.md b/README.md
@@ -4,6 +4,7 @@ This software works on Windows XP SP3, Windows 7+
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 [![Build Status](https://travis-ci.org/GerryFerdinandus/bittorrent-tracker-editor.svg?branch=master)](https://travis-ci.org/GerryFerdinandus/bittorrent-tracker-editor)
+for Windows, Linux and Mac build.
 
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