Add contributing part

README.md

@@ -34,6 +34,7 @@ A Node.js client library for [OneSignal](https://onesignal.com/) API.
   * [CSV Export](#csv-export)      
   * [Open track](#open-track)      
 * [Tests](#tests)
+* [Contributing](#contributing)
       
 ## Installation      
       
@@ -481,6 +482,19 @@ Running all tests:
 ```bash      
 $ npm test      
 ```      
+## Contributing
+
+### TL;DR
+
+To send a pull request:  
+ - Fork the repo  
+ - Clone the forked repo on your computer  
+ - Switch to develop branch  
+ - Create a feature branch (`git checkout -b feature/new-feature-name`)  
+ - Make your changes and add new tests if necessary  
+ - Run tests using `npm test`  
+ - Push your changes to your fork  
+ - Open a pull request
 
 ## License