update with comments

Author: luotao1

paddle/fluid/operators/elementwise_op.h

@@ -94,7 +94,7 @@ For example:
 
     shape(X) = (2, 3, 4, 5), shape(Y) = (,)
     shape(X) = (2, 3, 4, 5), shape(Y) = (5,)
-    shape(X) = (2, 3, 4, 5), shape(Y) = (4, 5)
+    shape(X) = (2, 3, 4, 5), shape(Y) = (4, 5), with axis=-1(default) or axis=2
     shape(X) = (2, 3, 4, 5), shape(Y) = (3, 4), with axis=1
     shape(X) = (2, 3, 4, 5), shape(Y) = (2), with axis=0
     shape(X) = (2, 3, 4, 5), shape(Y) = (2, 1), with axis=0

python/paddle/fluid/layers/nn.py

@@ -1409,7 +1409,7 @@ def sequence_pool(input, pool_type):
 
 def sequence_first_step(input):
     """
-    This function get the first step of sequence.
+    This function gets the first step of sequence.
 
     .. code-block:: text
 
@@ -1442,7 +1442,7 @@ def sequence_first_step(input):
 
 def sequence_last_step(input):
     """
-    This function get the last step of sequence.
+    This function gets the last step of sequence.
 
     .. code-block:: text