Add a brief documentation to README.md

This adds the very basic documentation about this model,
and also explains how to use it.

Signed-off-by: Fujimoto Seiji <fujimoto@ceptord.net>

README.md

@@ -1,3 +1,44 @@
----
-license: apache-2.0
----
+---
+license: apache-2.0
+language:
+- ja
+tags:
+- automatic-speech-recognition
+---
+
+# reazonspeech-k2-v2
+
+`reazonspeech-k2-v2` is an automatic speech recognition (ASR) model
+trained on [ReazonSpeech v2.0 corpus](https://huggingface.co/datasets/reazon-research/reazonspeech).
+
+This model provides end-to-end Japanese speech recognition based on
+[Next-gen Kaldi](https://k2-fsa.org/).
+
+## Model Architecture
+
+* Character-based RNN-T model. The total parameter count is 159.34M.
+
+* This model utilizes an enhanced Transformer architecture called
+  [Zipformer](https://arxiv.org/abs/2310.11230).
+
+* The training recipe is available on
+  [k2-fsa/icefall](https://github.com/k2-fsa/icefall/tree/master/egs/reazonspeech/ASR).
+
+## Usage
+
+We recommend to use this model through our
+[reazonspeech](https://github.com/reazon-research/reazonspeech)
+library.
+
+```
+from reazonspeech.k2.asr import load_model, transcribe, audio_from_path
+
+audio = audio_from_path("speech.wav")
+model = load_model()
+ret = transcribe(model, audio)
+print(ret.text)
+```
+
+## License
+
+[Apaceh Licence 2.0](https://choosealicense.com/licenses/apache-2.0/)