Add custom_main.js guide to documentation

docs/Using/Custom_main.md

@@ -0,0 +1,74 @@
+# Using custom_main.js
+
+This guide explains how to include and use a `custom_main.js` file in your Electron.NET application for advanced Electron/Node.js customization.
+
+## Why use custom_main.js?
+
+- Add custom Electron features (global shortcuts, tray icons, menus, etc.)
+- Integrate Node.js modules (e.g., telemetry, OS APIs)
+- Control startup logic (abort, environment checks)
+- Set up IPC messaging or preload scripts
+
+## Step-by-Step Process
+
+### 1. Create the custom_main.js file
+
+Place your custom logic in `electron/custom_main.js`:
+
+```javascript
+module.exports.onStartup = function(host) {
+    // Example: Register a global shortcut for opening dev tools
+    const { app, globalShortcut, BrowserWindow } = require('electron');
+    app.on('ready', () => {
+        const ret = globalShortcut.register('Control+Shift+I', () => {
+            BrowserWindow.getAllWindows().forEach(win => win.webContents.openDevTools());
+            console.log('Ctrl+Shift+I is pressed: DevTools opened!');
+        });
+    });
+    app.on('will-quit', () => {
+        globalShortcut.unregisterAll();
+    });
+    return true;
+};
+```
+
+### 2. Configure your .csproj to copy custom_main.js to output
+
+Add this to your `.csproj` file:
+
+```xml
+<ItemGroup>
+  <None Update="electron\custom_main.js">
+    <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    <TargetPath>.electron\custom_main.js</TargetPath>
+  </None>
+</ItemGroup>
+```
+
+### 3. Build and run your app
+
+Use the standard build/run commands:
+
+```powershell
+dotnet build
+dotnet run
+```
+
+Electron.NET will automatically load and execute your `custom_main.js` before initializing the .NET backend.
+
+## Advanced Usage
+
+Use environment variables to control features:
+
+  ```javascript
+  const env = process.env.ASPNETCORE_ENVIRONMENT || 'Production';
+  if (env === 'Development') { /* enable dev features */ }
+  ```
+
+## Notes
+
+- `custom_main.js` must use CommonJS syntax (`module.exports.onStartup = ...`).
+- Place the file in your source directory and copy it to `.electron` using `.csproj`.
+- Electron.NET will abort startup if `onStartup` returns `false`.
+
+### Complete example is available here [ElectronNetSampleApp](https://github.com/niteshsinghal85/ElectronNetSampleApp)

docs/_Sidebar.md

@@ -23,6 +23,7 @@
 - [Startup-Methods](Using/Startup-Methods.md)
 - [Debugging](Using/Debugging.md)
 - [Package Building](Using/Package-Building.md)
+- [Custom Main](Using/Custom_main.md)
 
 # API Reference