feat(nginx): 添加 SSL 证书配置

- 在 nginx.conf 中添加 SSL 证书路径
- 更新 README.md，说明 SSL 证书文件的要求

www/default/nginx.conf

@@ -27,6 +27,10 @@ server {
     listen 443 ssl default_server;
     listen [::]:443 ssl default_server;
 
+    # ssl 设置
+    ssl_certificate /etc/nginx/ssl/fullchain.pem;
+    ssl_certificate_key /etc/nginx/ssl/privkey.pem;
+
     #
     # Note: You should disable gzip for SSL traffic.
     # See: https://bugs.debian.org/773332