Merge pull request #810 from Jackwaterveg/doc

Add doc: ds2 online and ds2 offline

doc/src/released_model.md

 # Released Models
 
+## Acoustic Model Released
+Acoustic Model | Training Data | Token-based | Size | Descriptions | CER  | Hours of speech
+:-------------:| :------------:| :-----: | -----: | :----------------- | :---------- | :---------
+[Ds2 Online Aishell Model](https://deepspeech.bj.bcebos.com/release2.1/aishell/s0/aishell.s0.ds_online.5rnn.debug.tar.gz) | Aishell Dataset | Char-based | 345 MB  | 2 Conv + 5 LSTM layers with only forward direction | 0.0824 | 151 h
+[Ds2 Offline Aishell Model](https://deepspeech.bj.bcebos.com/release2.1/aishell/s0/aishell.s0.ds2.offline.cer6p65.release.tar.gz)| Aishell Dataset | Char-based | 306 MB | 2 Conv + 3 bidirectional gru layers| 0.065 | 151 h
+
+
 ## Language Model Released
 
 Language Model | Training Data | Token-based | Size | Descriptions