add feed infershape todo

paddle/operators/feed_op.h

@@ -31,6 +31,9 @@ class FeedKernel : public framework::OpKernel<T> {
         g_feed_variable->Get<std::vector<framework::Tensor>>();
     int col = ctx.template Attr<int>("col");
     PADDLE_ENFORCE_GT(tensors.size(), static_cast<size_t>(col));
+    // TODO(qijun):
+    //   check tensors[col].dims() with attribute,
+    //   except the first dimenson.
     out->CopyFrom<T>(tensors[col], ctx.GetPlace());
   }
 };