Update ADVANCED.md

Author: ruotianluo

ADVANCED.md

@@ -2,6 +2,12 @@
 
 ## Ensemble
 
+Current ensemble only supports models which are subclass of AttModel. Here is example of the script to run ensemble models. The `eval_ensemble.py` assumes the model saving under `log_$id`.
+
+```
+python eval_ensemble.py --dump_json 0 --ids model1,model2,model3 --weights 0.3,0.3,0.3 --batch_size 1 --dump_images 0 --num_images 5000 --split test --language_eval 1 --beam_size 5 --temperature 1.0 --sample_method greedy --max_length 30
+```
+
 ## Batch normalization
 
 ## Box feature