[ROOT-10544] Fix code example for TTreeReader
[ROOT-10544] Fix code example for TTreeReader

karies/root,root-mirror/root,olifre/root,karies/root,root-mirror/root,root-mirror/root,karies/root,olifre/root,karies/root,olifre/root,karies/root,olifre/root,root-mirror/root,root-mirror/root,karies/root,olifre/root,karies/root,root-mirror/root,olifre/root,root-mirror/root,root-mirror/root,karies/root,olifre/root,olifre/root,karies/root,olifre/root,olifre/root,root-mirror/root,karies/root,root-mirror/root,karies/root,root-mirror/root,olifre/root