Update BT.md

BT.md

@@ -1 +1,3 @@
+密钥为环境变量SESSION_SECRET
+
 ![8285bba413e770fe9620f1bf9b40d44e](https://github.com/user-attachments/assets/7a6fc03e-c457-45e4-b8f9-184508fc26b0)