Update README

Author: minhqngo

README.md

@@ -156,4 +156,8 @@ See `examples/run_mnist_multiclass.py` for a complete example of training a LeNe
 
 ```bash
 python examples/run_mnist_multiclass.py --backend gpu --batch_size 32 --epochs 10 --lr 0.01
-```
+```
+
+## TODO
+- Implement vanilla RNN layer
+- Implement Adam optimizer