docs: add contribution guide for device mode integration

CONTRIBUTING.md

@@ -51,6 +51,135 @@ To contribute to this project, you may need to install RudderStack on your machi
 For any questions, concerns, or queries, you can start by asking a question on our [**Slack**](https://rudderstack.com/join-rudderstack-slack-community/) channel.
 <br><br>
 
+----
+# Guide to develop your first device mode RudderStack integration
+
+Before diving into RudderStack integration development, it's essential to understand the [RudderStack Event Specification](https://www.rudderstack.com/docs/event-spec/standard-events/). This specification serves as the foundation for collecting data in a consistent format and then transforming data for the target destinations. In this guide, we'll focus specifically on developing a destination integration in device mode integration type.
+
+## Understanding integration types
+RudderStack supports two primary integration modes:
+
+1. **Cloud Mode Integration**: Events are routed through the RudderStack data plane in this mode
+2. **Device Mode Integration**: Events are sent directly from the client to the destination in this mode
+
+## Integration development journey
+
+### 1. Initial setup and configuration
+First, you'll need to configure the RudderStack UI in the [`rudder-integrations-config`](https://github.com/rudderlabs/rudder-integrations-config) repository:
+- Navigate to [`src/configurations/destinations`](./src/configurations/destinations)
+- Add necessary configuration files for dashboard setup
+- Prepare integration documentation or planning documents
+
+### 2. Core development steps
+
+#### Setting up the development environment
+```bash
+# Clone the repository
+git clone https://github.com/rudderlabs/rudder-sdk-js
+# Setup the project
+npm run setup
+```
+
+#### Essential components
+Your integration will require several key files:
+
+1. **Constants definition** (`/packages/analytics-js-common/src/constants/integrations`)
+   - Integration name
+   - Display name
+   - Directory name
+
+2. **Main integration code** (`packages/analytics-js-integrations/src/integrations`)
+   ```javascript
+   // index.js and browser.js structure
+   class TestIntegrationOne {
+     constructor(config, analytics, destinationInfo) {
+       // initialization code
+     }
+
+     init() {
+       // SDK initialization
+     }
+
+     // Core methods
+     isLoaded() { /**Your destination SDK is loaded successfully**/}
+     isReady() { /**At this point, you can start sending supported events to your destination e.g. track, identify, etc.**/ }
+
+     // Event handling
+     identify(rudderElement) {}
+     track(rudderElement) {}
+     page(rudderElement) {}
+     alias(rudderElement) {}
+     group(rudderElement) {}
+   }
+   ```
+
+### 3. Building and testing
+
+#### Build process
+```bash
+# For legacy build
+npm run build:integration --environment INTG_NAME:TestIntegrationOne
+
+# For modern build
+npm run build:integration:modern --environment INTG_NAME:TestIntegrationOne
+```
+
+#### Testing setup
+1. Serve the bundle:
+   ```bash
+   npx serve dist/cdn/js-integrations
+   ```
+2. Configure test environment:
+   - Modify `public/index.html` for mock source config
+   - Set environment variables (WRITE_KEY, DATAPLANE_URL)
+   - Run `npm run start`
+
+### 4. Automated testing
+Implement automated tests for your integration:
+```bash
+# Run tests for specific destination
+npm run test:ts -- component --destination=my_destination
+```
+
+### 5. UI configuration
+Two approaches for adding UI configurations:
+
+1. **Manual configuration**
+   - Add config files in `src/configurations/destinations`
+   - Use existing templates as reference
+
+2. **Automated generation**
+   ```bash
+   python3 scripts/configGenerator.py <path-to-placeholder-file>
+   ```
+
+## Deployment and support
+Once development is complete:
+1. The RudderStack team will handle production deployment
+2. An announcement will be made in the [Release Notes](https://www.rudderstack.com/docs/releases/) and Slack `#product-releases` channel
+3. Ongoing support is available through:
+   - GitHub PR feedback
+   - [RudderStack Slack community](https://rudderstack.com/join-rudderstack-slack-community/) `#contributing-to-rudderstack` channel
+
+## Best practices
+- Draft the integration plan document before coding
+- Be judicious in choosing where you want to allow integration users to configure settings (in the control plane vs the sdk instrumentation code)
+- Follow existing integration examples
+- Document all configuration options
+- Keep code modular and maintainable
+
+Building a RudderStack integration requires attention to detail and thorough testing. The RudderStack team provides support throughout the development process, ensuring your integration meets quality standards and works reliably in production.
+
+## References
+
+- [RudderStack community on Slack](https://rudderstack.com/join-rudderstack-slack-community/)
+- [Recording of the community workshop to develop device mode integration](https://youtu.be/70w2ESMBPCI)
+- [Guide to develop source and cloud mode destination integration](https://github.com/rudderlabs/rudder-transformer/blob/develop/CONTRIBUTING.md)
+- [Recording of the community workshop to develop source and cloud mode integration](https://youtu.be/OD2vCYG-P7k)
+- [RudderStack Event Specification](https://www.rudderstack.com/docs/event-spec/standard-events/)
+
+----
+
 ### We look forward to your feedback on improving this project!
 
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