docs: fix broken contribution link in README; add screenshot (#3211)

README.md

@@ -9,7 +9,6 @@
 <a href="https://github.styleci.io/repos/28257573"><img src="https://github.styleci.io/repos/28257573/shield?style=flat" alt="StyleCI"></a>
 </p>
 
-
 ## About Flarum
 
 **[Flarum](https://flarum.org/) is a delightfully simple discussion platform for your website.** It's fast and easy to use, with all the features you need to run a successful community. It is designed to be:
@@ -20,13 +19,15 @@
 
 * **Powerful and extensible.** Customize, extend, and integrate Flarum to suit your community. Flarum’s architecture is amazingly flexible, with a powerful Extension API.
 
+![Screenshot of a Flarum instance, showing multiple discussions and tags.](https://flarum.org/assets/img/home-screenshot.png)
+
 ## Installation
 
-This repository contains Flarum's core code. If you want to set up a forum, visit the [Flarum skeleton repository](https://github.com/flarum/flarum).
+This repository contains Flarum's core code. If you want to set up a forum, visit the [Flarum skeleton repository](https://github.com/flarum/flarum). For support, refer to the [documentation](https://docs.flarum.org/), and ask questions on [Flarum Discuss](https://discuss.flarum.org/) (our community forum) or [Discord server](https://flarum.org/discord/).
 
 ## Contributing
 
-Thank you for considering contributing to Flarum! Please read the **[Contributing guide](https://flarum.org/docs/contributing.html)** to learn how you can help.
+Thank you for considering contributing to Flarum! Please read the **[Contributing guide](https://docs.flarum.org/contributing)** to learn how you can help.
 
 ## Security Vulnerabilities