[RN] Add Stephan to the 6.16 contributors.

README/ReleaseNotes/v616/index.md

@@ -43,6 +43,7 @@ The following people have contributed to this new version:
  Xavier Valls, CERN/SFT,\
  Vassil Vassilev, Princeton/CMS,\
  Wouter Verkerke, NIKHEF/Atlas,\
+ Stephan Hageboeck, CERN/SFT,\
  Stefan Wunsch, CERN/SFT
 
 ## Deprecation and Removal