[relnotes] add info. about RooLagrangianMorphFunc
[relnotes] add info. about RooLagrangianMorphFunc

Co-authored-by: Jonas Rembser <800b99c85294e2c58da2b9acf2b7784ff891e048@cern.ch>

olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root