add subtle hint about api docs in tutorial
add subtle hint about api docs in tutorial

bastings/neuralmonkey,bastings/neuralmonkey,juliakreutzer/bandit-neuralmonkey,ufal/neuralmonkey,ufal/neuralmonkey,bastings/neuralmonkey,juliakreutzer/bandit-neuralmonkey,juliakreutzer/bandit-neuralmonkey,bastings/neuralmonkey,bastings/neuralmonkey,juliakreutzer/bandit-neuralmonkey,ufal/neuralmonkey,juliakreutzer/bandit-neuralmonkey,ufal/neuralmonkey,ufal/neuralmonkey