docs: document pyroscope env var

.env.example

@@ -14,6 +14,8 @@
 # PYROSCOPE_APP_NAME=new-api
 # PYROSCOPE_BASIC_AUTH_USER=your-user
 # PYROSCOPE_BASIC_AUTH_PASSWORD=your-password
+# PYROSCOPE_MUTEX_RATE=5
+# PYROSCOPE_BLOCK_RATE=5
 # HOSTNAME=your-hostname
 
 # 数据库相关配置