[TMVA] Add keras tutorials to documentation

They were missing a crucial comment header, making the documentation
generation system not pick them up.

tutorials/tmva/keras/ApplicationClassificationKeras.py

 #!/usr/bin/env python
+## \file
+## \ingroup tutorial_tmva
+## \notebook -nodraw
+## This tutorial shows how to apply a trained model to new data.
+##
+## \macro_code
+##
+## \date 2017
+## \author TMVA Team
 
 from ROOT import TMVA, TFile, TString
 from array import array

tutorials/tmva/keras/ApplicationRegressionKeras.py

 #!/usr/bin/env python
+## \file
+## \ingroup tutorial_tmva
+## \notebook -nodraw
+## This tutorial shows how to apply a trained model to new data (regression).
+##
+## \macro_code
+##
+## \date 2017
+## \author TMVA Team
 
 from ROOT import TMVA, TFile, TString
 from array import array

tutorials/tmva/keras/ClassificationKeras.py

 #!/usr/bin/env python
+## \file
+## \ingroup tutorial_tmva
+## \notebook -nodraw
+## This tutorial shows how to do classification in TMVA with neural networks
+## trained with keras.
+##
+## \macro_code
+##
+## \date 2017
+## \author TMVA Team
 
 from ROOT import TMVA, TFile, TTree, TCut
 from subprocess import call

tutorials/tmva/keras/GenerateModel.py

 #!/usr/bin/env python
+## \file
+## \ingroup tutorial_tmva
+## \notebook -nodraw
+## This tutorial shows how to define and generate a keras model for use with
+## TMVA.
+##
+## \macro_code
+##
+## \date 2017
+## \author TMVA Team
 
 from keras.models import Sequential
 from keras.layers.core import Dense, Activation

tutorials/tmva/keras/MulticlassKeras.py

 #!/usr/bin/env python
+## \file
+## \ingroup tutorial_tmva
+## \notebook -nodraw
+## This tutorial shows how to do multiclass classification in TMVA with neural
+## networks trained with keras.
+##
+## \macro_code
+##
+## \date 2017
+## \author TMVA Team
 
 from ROOT import TMVA, TFile, TTree, TCut, gROOT
 from os.path import isfile

tutorials/tmva/keras/RegressionKeras.py

 #!/usr/bin/env python
+## \file
+## \ingroup tutorial_tmva
+## \notebook -nodraw
+## This tutorial shows how to do regression in TMVA with neural networks
+## trained with keras.
+##
+## \macro_code
+##
+## \date 2017
+## \author TMVA Team
 
 from ROOT import TMVA, TFile, TTree, TCut
 from subprocess import call