add examples for slicing option (apache#11918)

src/operator/tensor/indexing_op.cc

@@ -570,6 +570,10 @@ Examples::
   indices = [[1, 1, 0], [0, 1, 0]]
   gather_nd(data, indices) = [2, 3, 0]
 
+  data = [[[1, 2], [3, 4]], [[5, 6], [7, 8]]]
+  indices = [[0, 1], [1, 0]]
+  gather_nd(data, indices) = [[3, 4], [5, 6]]
+
 )code")
 .set_num_outputs(1)
 .set_num_inputs(2)
@@ -629,6 +633,21 @@ Examples::
   shape = (2, 2)
   scatter_nd(data, indices, shape) = [[0, 0], [2, 3]]
 
+  data = [[[1, 2], [3, 4]], [[5, 6], [7, 8]]]
+  indices = [[0, 1], [1, 1]]
+  shape = (2, 2, 2, 2)
+  scatter_nd(data, indices, shape) = [[[[0, 0],
+                                        [0, 0]],
+
+                                       [[1, 2],
+                                        [3, 4]]],
+
+                                      [[[0, 0],
+                                        [0, 0]],
+
+                                       [[5, 6],
+                                        [7, 8]]]]
+
 )code")
 .set_num_outputs(1)
 .set_num_inputs(2)