Add Electron example for PSPDFKit integration

- Created a new Electron example project demonstrating the integration of PSPDFKit.
- Added essential files including package.json, README.md, and configuration files for Electron setup.
- Implemented a basic layout with a PDF viewer using PSPDFKit, allowing users to open and view PDF documents.
- Included scripts for managing file imports and exports, along with drag-and-drop functionality.
- Added sample assets including a default PDF document and application icons for different platforms.
- Introduced .gitignore to exclude unnecessary files and directories.
- Provided detailed instructions in the README for getting started and running the example.

Author: ritz078

examples/electron-nodeintegration/.gitignore

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+node_modules
+release-builds
+dist

examples/electron-nodeintegration/README.md

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+# PSPDFKit for Electron Example App
+
+This example shows how to build a [PSPDFKit for Electron](https://www.nutrient.io/electron/) application with
+[Electron](https://electronjs.org/).
+
+This example uses node integration. If you're looking for an example with context isolation enabled, and node integration disabled, you can switch to the [`master` branch](https://github.com/PSPDFKit/pspdfkit-electron-example/tree/master).
+
+## Prerequisites
+
+- [Node.js](http://nodejs.org/)
+
+## Support and Issues
+
+Are you [evaluating our SDK](https://www.nutrient.io/try/)? That's great, we're happy to help out! To make sure this is fast, please use a work email and have someone from your company fill out our sales form: https://www.nutrient.io/sales/
+
+## Getting Started
+
+Clone the repo:
+
+```bash
+git clone https://github.com/PSPDFKit/pspdfkit-electron-example.git
+cd pspdfkit-electron-example
+```
+
+Install the project dependencies with `npm`:
+
+```bash
+npm install
+```
+
+**Important:** If you are using Windows, do not use PowerShell. Instead, use Microsoft’s [Developer Command Prompt for Visual Studio](https://docs.microsoft.com/en-us/dotnet/framework/tools/developer-command-prompt-for-vs).
+
+## Running the Example
+
+We are ready to launch the app! 🎉
+
+```bash
+npm run start
+```
+
+The Electron application will automatically start.
+
+To open the developer tools inside Electron, uncomment the following line in `index.js`:
+
+```js
+// Open the DevTools.
+mainWindow.webContents.openDevTools();
+```
+
+## What's in This Repository
+
+This repository contains an example integration of [PSPDFKit for Electron](https://www.nutrient.io/electron). The project structure is influenced by the default Electron example app and comes with the following files:
+
+| Filename          | Description                                                                                                                                                                                                                              |
+| ----------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| `src/index.js`    | The main entry point used to create the Electron windows. This file does not contain major changes, with the exception of a validation to make sure that PSPDFKit is properly installed. It is responsible for loading `src/index.html`. |
+| `src/index.html`  | The main HTML entry point. It will set up a simple HTML structure and invoke the JavaScript that runs in the renderer thread: `src/renderer.js`.                                                                                         |
+| `src/renderer.js` | This file is where we import PSPDFKit and set it up properly. We use it to extend Nutrient Web SDK with custom behavior.                                                                                                                 |
+
+## Build Production Packages
+
+We recommend using [`electron-packager`](https://github.com/electron-userland/electron-packager) or a similar solution to build the production bundles.
+
+### Install `electron-packager`
+
+```bash
+npm install -g electron-packager
+```
+
+### Build Individual Packages
+
+The following code will only work on macOS. For other platforms, please consult the [documentation](https://github.com/electron-userland/electron-packager#electron-packager) of `electron-packager`:
+
+```bash
+npm run package-mac-intel
+npm run package-mac-apple (Apple Silicon)
+npm run package-win (requires Wine: `brew cask install xquartz`, `brew install wine`)
+npm run package-linux (requires `apt-get install libgconf-2-4` on target Linux)
+```
+
+## License
+
+This software is licensed under a [modified BSD license](LICENSE).
+
+## Contributing
+
+Please ensure
+[you have signed our CLA](https://www.nutrient.io/guides/web/current/miscellaneous/contributing/) so that we can
+accept your contributions.