docs: add v5 migration guide with installation screenshots and steps

Author: msanatan

MCPForUnity/Editor/Windows/MCPForUnityEditorWindow.cs

@@ -45,7 +45,6 @@ public class MCPForUnityEditorWindow : EditorWindow
         // UI state
         private int selectedClientIndex = 0;
 
-        [MenuItem("Window/MCP For Unity")]
         public static void ShowWindow()
         {
             GetWindow<MCPForUnityEditorWindow>("MCP For Unity");

docs/screenshots/v5_01_uninstall.png

@@ -0,0 +1,54 @@
+# MCP for Unity v5 Migration Guide
+
+This guide will help you migrate from the legacy UnityMcpBridge installation to the new MCPForUnity package structure in version 5.
+
+## Overview
+
+Version 5 introduces a new package structure. The package is now installed from the `MCPForUnity` folder instead of the legacy `UnityMcpBridge` folder.
+
+## Migration Steps
+
+### Step 1: Uninstall the Current Package
+
+1. Open the Unity Package Manager (**Window > Package Manager**)
+2. Select **Packages: In Project** from the dropdown
+3. Find **MCP for Unity** in the list
+4. Click the **Remove** button to uninstall the legacy package
+
+![Uninstalling the legacy package](screenshots/v5_01_uninstall.png)
+
+### Step 2: Install from the New Path
+
+1. In the Package Manager, click the **+** button in the top-left corner
+2. Select **Add package from disk...**
+3. Navigate to the `MCPForUnity` folder (NOT the old `UnityMcpBridge` folder)
+4. Select the `package.json` file inside the `MCPForUnity` folder
+5. Click **Open** to install the package
+
+![Installing from the new MCPForUnity path](screenshots/v5_02_install.png)
+
+### Step 3: Rebuild MCP Server
+
+After installing the new package, you need to rebuild the MCP server:
+
+1. In Unity, go to **Window > MCP for Unity > Open MCP Window**
+![Opening the MCP window](screenshots/v5_03_open_mcp_window.png)
+2. Click the **Rebuild MCP Server** button
+![Rebuilding the MCP server](screenshots/v5_04_rebuild_mcp_server.png)
+3. You should see a success message confirming the rebuild
+![Rebuild success](screenshots/v5_05_rebuild_success.png)
+
+## Verification
+
+After completing these steps, verify the migration was successful:
+
+- Check that the package appears in the Package Manager as **MCP for Unity**
+- Confirm the package location shows the new `MCPForUnity` path
+- Test basic MCP functionality to ensure everything works correctly
+
+## Troubleshooting
+
+- Check the Unity Console for specific error messages
+- Ensure Python dependencies are properly installed
+- Try pressing the rebuild button again
+- Try restarting Unity and repeating the installation steps