update README

Author: shaojieb

README.md

@@ -18,6 +18,8 @@ Experiments are done in PyTorch. If you find this repository helpful, please cit
 
 ## Domains and Datasets
 
+**Update**: The code should be directly runnable with PyTorch 0.4.0 or above (PyTorch 1.0 strongly recommended). The older versions of PyTorch are no longer supported.
+
 This repository contains the benchmarks to the following tasks, with details explained in each sub-directory:
 
   - **The Adding Problem** with various T (we evaluated on T=200, 400, 600)