add notes on future / draft posts

Author: gasparnagy

CONTRIBUTING.md

@@ -20,4 +20,6 @@ In order to test your changes, there are multiple options:
   * This will host the site at http://127.0.0.1:4000/
 * Build the site once
   * Invoke `bundle exec jekyll build`
-  * The generated site is in the `_site` folder
+  * The generated site is in the `_site` folder
+
+In order to create draft posts, you can find ideas in [this article by Fizer Khan](https://www.fizerkhan.com/blog/posts/working-with-upcoming-posts-in-jekyll). You can force displaying future posts with the `--future` flag (e.g. `bundle exec jekyll serve --livereload --future`).