Added release notes for v104r2

ReleaseNotes/v104r2.md

+2018-06-14 Geant4 v104r2
+===
+This release is based on `GEANT4 r10.4.2`, uses `LCG 93` and `Geant4Files v104r1`.
+
+This version is released on `Sim10` branch.
+
+## Latest Changes
+
+#### LHCb G4 Tests
+**[MR !35] Fixed compilation warnings in G4RichTbSimHTest**