message: add comment with documentation on jet rho estimation
diff: @@ -4411,6 +4411,9 @@ void AliIsolationCut::MakeIsolationCut
  else if ( fICMethod == kSumBkgSubJetRhoIC )
  {
  // Rely on Jet group methods to get the UE density.
  + // https://alice-notes.web.cern.ch/system/files/notes/analysis/178/2015-Mar-02-analysis_note-fulltext.pdf
  + // "normal" rho approach is Sec. 5.1.1, sparse event 5.1.2
  +
  AliRhoParameter * outrho = (AliRhoParameter*) reader->GetInputEvent()->FindListObject(fJetRhoTaskName);
  if ( !outrho )
  