[ntuple][doc] Add RNTupleModel::MakeField examples
[ntuple][doc] Add RNTupleModel::MakeField examples

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