Add: Instructions to preview changes on netlify (#22)

Author: RaiVaibhav

CONTRIBUTING.md

@@ -34,6 +34,13 @@ In general we'd like to ask you to please target the master branch with your pul
 We recommend creating a new branch for each feature task/bug since it makes easier to edit
 commits in future if needed.
 
+After submitting a pull request, preview your changes by going through the `Checks` tab and click `Pages changed` under `Netlify` checks then under `DETAILS` section click `view` to preview
+any changed page
+
+![Changed pages](https://user-images.githubusercontent.com/22278438/55508576-cfdd6200-5677-11e9-9b27-8d2ae823f1b5.png)
+
+
+
 ## Reviewing Issues and Pull Requests
 
 You're welcome to review issues and pull requests, provide feedback, and answer questions.