Update README.md to increase QR code visibility for WeChat appreciation

- Enlarged the WeChat appreciation QR code image from 300px to 500px for better visibility.
- Maintained the accompanying text to encourage user support and engagement.
- Continued improvements to the layout for a more user-friendly experience.

README.md

@@ -210,7 +210,7 @@ You've reached your trial request limit.
 </td>
 <td align="center">
 <b>微信赞赏</b><br>
-<img src="img/wx_zsm2.png" width="300" alt="微信赞赏码"><br>
+<img src="img/wx_zsm2.png" width="500" alt="微信赞赏码"><br>
 <small>要到饭咧？啊咧？啊咧？不给也没事~ 请随意打赏</small>
 </td>
 <td align="center">