docs: update WeChat group 16 QR code (#318)

README.md

@@ -236,7 +236,7 @@ You're also welcome to join our **GenericAgent Community Group** for discussion,
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-      <td align="center"><strong>WeChat Group 15</strong><br><img src="assets/images/wechat_group15.jpg" alt="WeChat Group 15 QR Code" width="250"/></td>
+      <td align="center"><strong>WeChat Group 16</strong><br><img src="assets/images/wechat_group16.jpg" alt="WeChat Group 16 QR Code" width="250"/></td>
     </tr>
   </table>
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@@ -550,7 +550,7 @@ GenericAgent 通过**分层记忆 × 最小工具集 × 自主执行循环**完
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-      <td align="center"><strong>微信群 15</strong><br><img src="assets/images/wechat_group15.jpg" alt="微信群 15 二维码" width="250"/></td>
+      <td align="center"><strong>微信群 16</strong><br><img src="assets/images/wechat_group16.jpg" alt="微信群 16 二维码" width="250"/></td>
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 </div>