Add `downloadSettings` for H2 (#204)

VLESS-XHTTP3-Nginx/client.jsonc

@@ -30,13 +30,27 @@
         "network": "xhttp",
         "xhttpSettings": {
           "path": "", //填写你的 path
-          "mode": "stream-one",
+          "mode": "stream-one", //如使用 downloadSettings（下行），不可用 stream-one；可用 stream-up。
           "xmux": {
             "maxConcurrency": 128, //Nginx 默认上限 128。https://nginx.org/en/docs/http/ngx_http_v3_module.html#http3_max_concurrent_streams
             "hMaxRequestTimes": 1000, //Nginx 默认上限 1000。https://nginx.org/en/docs/http/ngx_http_core_module.html#keepalive_requests
             "cMaxLifetimeMs": 3600000 //Nginx 默认上限 3600000ms(1h)。https://nginx.org/en/docs/http/ngx_http_core_module.html#keepalive_time
+          },
+          "#downloadSettings": { //如需 H2 下行：移除前面的 #（井号）以使用 downloadSettings；上面的 mode 更改为 stream-up。
+            "address": "example.com",
+            "port": 443,
+            "network": "xhttp",
+            "xhttpSettings": {
+              "path": "", //填写你的 path（同上）
+              "xmux": {
+                "maxConcurrency": 128, //Nginx 默认上限 128。https://nginx.org/en/docs/http/ngx_http_v3_module.html#http3_max_concurrent_streams
+                "hMaxRequestTimes": 1000, //Nginx 默认上限 1000。https://nginx.org/en/docs/http/ngx_http_core_module.html#keepalive_requests
+                "cMaxLifetimeMs": 3600000 //Nginx 默认上限 3600000ms(1h)。https://nginx.org/en/docs/http/ngx_http_core_module.html#keepalive_time
+              }
+            },
+            "security": "tls"
           }
-        }
+        },
         "security": "tls",
         "tlsSettings": {
           "alpn": [