update docs save / load npz

Author: zsdonghao

docs/modules/files.rst

@@ -9,21 +9,22 @@ sake of cross-platform.
 
 .. code-block:: python
 
-  # save model as .ckpt
+  ## save model as .ckpt
   saver = tf.train.Saver()
   save_path = saver.save(sess, "model.ckpt")
   # restore model from .ckpt
   saver = tf.train.Saver()
   saver.restore(sess, "model.ckpt")
 
-  # save model as .npz
+  ## save model as .npz
   tl.files.save_npz(network.all_params , name='model.npz')
-
-  # restore model from .npz
-  load_params = tl.files.load_npz(path='', name='model.npz')
+  # restore model from .npz (method 1)
+  load_params = tl.files.load_npz(name='model.npz')
   tl.files.assign_params(sess, load_params, network)
+  # restore model from .npz (method 2)
+  tl.files.load_and_assign_npz(sess=sess, name='model.npz', network=network)
 
-  # you can assign the pre-trained parameters as follow
+  ## you can assign the pre-trained parameters as follow
   # 1st parameter
   tl.files.assign_params(sess, [load_params[0]], network)
   # the first three parameters