add a separate headline for the testing paragraph

README.md

@@ -52,12 +52,14 @@ Now build and run - e.g. by pressing Cmd-r - or click on the triangle at the top
       if not yet implemented
       (cannot test currently, iphone-battery is empty))
 
-## Changelog
+## Testing
 
 Betas are distributed via Testflight.
 
 Please [send us a mail](mailto:ios@getdelta.org?subject=Testflight%20invite%20request&body=Hello,%0A%0APlease%20send%20me%20a%20Testflight%20invite%20for%20Deltachat%20iOS) if you also want to test the app.
 
+## Changelog
+
 ### Beta 3
 upcoming (not released)