docs: 增加说明

Author: geekact

README.md

@@ -1,6 +1,6 @@
 # foca-openapi
 
-使用openapi文档生成请求服务
+使用openapi文档生成请求服务。支持 **Openapi 3.0**
 
 [![npm peer typescript version](https://img.shields.io/npm/dependency-version/foca-openapi/peer/typescript?logo=typescript)](https://github.com/microsoft/TypeScript)
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