Add Windows 7 compatibility documentation to README

close #2

Author: SHIINASAMA

README.md

@@ -89,4 +89,5 @@ You also can use the command line to run the project.
 ## Others
 
 - [Release and Product Version Control](docs/publish.md)
-- [Internationalization](docs/i18n.md)
+- [Internationalization](docs/i18n.md)
+- [Windows 7 Compatibility](docs/windows7.md)

docs/windows7.md

@@ -0,0 +1,56 @@
+# Windows 7 Compatibility
+
+## Feature Integrity
+
+Due to system limitations on Windows 7, some features cannot be fully enabled on this platform.  
+The following list summarizes the confirmed missing or limited functionalities:
+
+### Theme-Related
+
+-   System theme synchronization is **not supported**; only manual switching between light and dark themes is available.
+    
+-   **HiDPI** (High DPI) display support is unavailable.
+    
+
+### Internationalization (I18N) String Collection
+
+-   Some older versions of **PySide6** do **not include** the `lupdate` executable, which prevents automatic collection of translation strings (generation of `.ts` files).
+    
+-   **Workaround:**  
+    Add the directory containing your custom `lupdate` executable to the system `PATH` environment variable, so that `pyside-cli` can detect it properly.
+    
+
+### Nuitka Build Backend
+
+-   Compilation and packaging with Nuitka are theoretically possible, but the generated applications **may fail to run properly** on Windows 7.
+    
+
+---
+
+## Usage Notes
+
+This project provides **PyInstaller** as a compatibility build backend for Windows 7.  
+You can enable this mode by adding the `--backend pyinstaller` flag when running commands:
+
+```bash
+uv run pyside-cli --all --onefile --backend pyinstaller --low-perf
+```
+
+### Build Recommendations
+
+Packaging on Windows 7 may encounter toolchain incompatibility issues.  
+It is recommended to follow one of the approaches below:
+
+1.  **Preferred approach:**  
+    Perform development and builds on a newer Windows platform, then test on the target Windows 7 system.
+    
+2.  **Alternative approaches:**
+    
+    -   Downgrade specific toolchain versions to regain compatibility.
+        
+    -   Use compatibility layers such as [VxKex](https://github.com/i486/VxKex) to run build tools.
+        
+
+Additionally, since Windows 7 often runs on older hardware,  
+it’s recommended to include the `--low-perf` flag in your build command to disable certain high-performance features,  
+improving overall stability and compatibility.