add open router provider doc

README.md

@@ -261,7 +261,24 @@ Transformers allow you to modify the request and response payloads to ensure com
 - `Anthropic`:If you use only the `Anthropic` transformer, it will preserve the original request and response parameters(you can use it to connect directly to an Anthropic endpoint).
 - `deepseek`: Adapts requests/responses for DeepSeek API.
 - `gemini`: Adapts requests/responses for Gemini API.
-- `openrouter`: Adapts requests/responses for OpenRouter API.
+- `openrouter`: Adapts requests/responses for OpenRouter API. It can also accept a `provider` routing parameter to specify which underlying providers OpenRouter should use. For more details, refer to the [OpenRouter documentation](https://openrouter.ai/docs/features/provider-routing). See an example below:
+  ```json
+    "transformer": {
+      "use": ["openrouter"],
+      "moonshotai/kimi-k2": {
+        "use": [
+          [
+            "openrouter",
+            {
+              "provider": {
+                "only": ["moonshotai/fp8"]
+              }
+            }
+          ]
+        ]
+      }
+    }
+  ```
 - `groq`: Adapts requests/responses for groq API.
 - `maxtoken`: Sets a specific `max_tokens` value.
 - `tooluse`: Optimizes tool usage for certain models via `tool_choice`.

README_zh.md

@@ -255,7 +255,24 @@ Transformers 允许您修改请求和响应负载，以确保与不同提供商
 -   `Anthropic`: 如果你只使用这一个转换器，则会直接透传请求和响应(你可以用它来接入其他支持Anthropic端点的服务商)。
 -   `deepseek`: 适配 DeepSeek API 的请求/响应。
 -   `gemini`: 适配 Gemini API 的请求/响应。
--   `openrouter`: 适配 OpenRouter API 的请求/响应。
+-   `openrouter`: 适配 OpenRouter API 的请求/响应。它还可以接受一个 `provider` 路由参数，以指定 OpenRouter 应使用哪些底层提供商。有关更多详细信息，请参阅 [OpenRouter 文档](https://openrouter.ai/docs/features/provider-routing)。请参阅下面的示例：
+    ```json
+      "transformer": {
+        "use": ["openrouter"],
+        "moonshotai/kimi-k2": {
+          "use": [
+            [
+              "openrouter",
+              {
+                "provider": {
+                  "only": ["moonshotai/fp8"]
+                }
+              }
+            ]
+          ]
+        }
+      }
+    ```
 -   `groq`: 适配 groq API 的请求/响应
 -   `maxtoken`: 设置特定的 `max_tokens` 值。
 -   `tooluse`: 优化某些模型的工具使用(通过`tool_choice`参数)。