环境变量使用说明添加

Author: wangle201210

README.md

@@ -19,9 +19,11 @@ go get github.com/wangle201210/text2sql
 
 ### 基本用法
 
+```bash
 export OPENAI_API_KEY="sk-******"
 export OPENAI_MODEL_NAME="gpt-4o-mini"
 export OPENAI_BASE_URL="https://api.openai.com/v1"
+```
 
 ```go
 package main