input: Write a python function to develop a neural network model in Python to recognize a hand-written number.
  assert isinstance(model, tf.keras.Model)
  assert model.input_shape == (None, 784)
  assert model.output_shape == (None, 10)
output: def create_model():
      import tensorflow as tf
      from tensorflow.keras import layers, models
      
      model = models.Sequential()
      model.add(layers.InputLayer(input_shape=(784,)))
      model.add(layers.Dense(512, activation='relu'))
      model.add(layers.Dense(256, activation='relu'))
      model.add(layers.Dense(10, activation='softmax'))
      
      model.compile(optimizer='adam', loss='sparse_categorical_crossentropy', metrics=['accuracy'])
      
      return model