Add contributing guideline link: align with skeleton [skip ci]

README.md

@@ -137,12 +137,9 @@ To use the Material theme, import the correspondent file from the `theme/materia
 We are using [ESLint](http://eslint.org/) for linting JavaScript code. You can check if your code is following our standards by running `gulp lint`, which will automatically lint all `.js` files as well as JavaScript snippets inside `.html` files.
 
 
-## Creating a pull request
+## Contributing
 
-  - Make sure your code is compliant with our code linters: `gulp lint`
-  - Check that tests are passing: `polymer test`
-  - [Submit a pull request](https://www.digitalocean.com/community/tutorials/how-to-create-a-pull-request-on-github) with detailed title and description
-  - Wait for response from one of Vaadin components team members
+  To contribute to the component, please read [the guideline](https://github.com/vaadin/vaadin-core/blob/master/CONTRIBUTING.md) first.
 
 
 ## License