updated ci page

contributing-ci.rst

@@ -1,8 +1,21 @@
 Continuous integration
 **********************
 
-* All pushes to our main repo @ https://github.com/zammad/zammad will trigger build test on https://travis-ci.org.
-* You can find the build results @ https://travis-ci.org/zammad/zammad
-* If you fork the Zammad repo you can use travis-ci.org to get your builds tested
+All pushes to our main repo @ https://github.com/zammad/zammad will trigger build tests. 
+We use internal build tests on internal and external continuous integration platforms.
+
+Internal
+========
+
+* Done in our private Continuous integration platform
+
+External
+========
+
+Travis-CI
+---------
+
+* You can find the build test results @ https://travis-ci.org/zammad/zammad
+* If you fork the Zammad repo you're able to also use travis-ci.org to get your builds tested
 * Just change the file ".travis.yml" to fit your needs