Added WindowHelpers page

Documentation/ui-helpers/windowhelpers.md

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+# WindowHelpers
+
+This page is about the `WindowHelpers` class available in [`PeyrSharp.UiHelpers`](../ui-helpers.md). This page is about all of its methods.
+
+## Compatibility
+
+WindowHelpers are part of the `PeyrSharp.UiHelpers` module, which is compatible with all of these frameworks and platforms:
+
+| Package/Platform | Windows    | macOS      | Linux + others |
+| ---------------- | ---------- | ---------- | -------------- |
+| UiHelpers        | ✅         | ❌         | ❌             |
+| **Framework**    | **.NET 5** | **.NET 6** | **.NET 7**     |
+| UiHelpers        | ✅         | ✅         | ✅             |
+
+## Methods
+
+### GetWindows()
+
+#### Definition
+
+Retrieves a list of currently visible windows.
+
+#### Returns
+
+A list of `WindowInfo` objects representing the visible windows.
+
+#### Usage
+
+```c#
+using PeyrSharp.UiHelpers;
+using System.Collections.Generic;
+
+public class MyWindowManager
+{
+    public void PrintOpenedWindows() {
+        List<WindowInfo> windows = WinFormsHelpers.GetWindows();
+        foreach (WindowInfo window in windows)
+        {
+            Console.WriteLine(window.Name);
+        }
+    }
+}
+```