docs: label the captcha example answer

State that the captcha image displayed in both model cards has the answer 9125.

README.md

@@ -35,6 +35,8 @@ contains the `PwVerifyCode` and `PwGDCode` classes targeted by this model.
 
 ![Example PHPWind captcha](assets/example_captcha.png)
 
+> **Answer for the captcha shown above:** `9125`
+
 ## Scope and responsible use
 
 This model is intended for PHPWind site operators, developers, and researchers

README_zh.md

@@ -34,6 +34,8 @@ metrics:
 
 ![PHPWind 验证码样例](assets/example_captcha.png)
 
+> **上图验证码的正确答案：** `9125`
+
 ## 适用范围与负责任使用
 
 本模型面向 PHPWind 站点的运营者、开发者及研究者，用于其自有或已获明确授权的