add api usage docs

PaddleNLP/README.md

@@ -73,6 +73,14 @@ roberta = RobertaModel.from_pretrained('roberta-wwm-ext')
 
 For more pretrained model selection, please refer to [PretrainedModels](./paddlenlp/transformers/README.md)
 
+## API Usage
+
+* Transformer API(./docs/transformers.md)
+* Dataset API(./docs/datasets.md)
+* Embedding API(./docs/embeddings.md)
+* Metrics API(./docs/embeddings.md)
+* Models API(./docs/models.md)
+
 ## Tutorials
 
 List our notebook tutorials based on AI Studio.
@@ -88,4 +96,4 @@ TBD
 
 ## License
 
-PaddleNLP is provided under the [Apache-2.0 License](./LICENSE).
+PaddleNLP is provided under the [Apache-2.0 License](./LICENSE).
\ No newline at end of file

PaddleNLP/README_cn.md

+# PaddleNLP 中文README

PaddleNLP/docs/datasets.md

+# paddlenlp.datasets集成的API清单
+
+以表格形式汇总，需要至少包含数据类型，数据介绍，数据API

PaddleNLP/docs/embeddings.md

+# Embedding 模型汇总
+
+包括中英文参数，表格形式汇总

PaddleNLP/docs/metrics.md

+# paddlenlp.metrics API汇总

PaddleNLP/docs/models.md

+# paddlenlp.models
+
+高阶组网API说明，Ernie, SimNet, Senta

PaddleNLP/docs/transformers.md

+# 汇总paddlenlp.transformer下预训练模型