doc: en unity quickstart.md (#216)

* docs: unity chinese sdk 3.8

* unity doc en sdk3.8

* unity: fix error

* doc:fix docusaurus-plugin-content-docs-sdks/current/quickstart/unity.mdx

Author: yj12138

i18n/en/docusaurus-plugin-content-docs-sdks/current/quickstart/unity.mdx

@@ -14,7 +14,8 @@ We strongly recommend running the framework-related example [DEMO](https://githu
 2. **Import Namespace**: Import the necessary namespace in your scripts:
 
     ```csharp
-    using open_im_sdk;
+    using OpenIM.IMSDK.Unity;
+    using OpenIM.IMSDK.Unity.Listener;
     ```
 
 3. **Initialize SDK**: