Docs for Siren (#4023)

This adds some documentation for the Siren app into the Lighthouse book.

Co-authored-by: Mavrik <mrricki.m.usmc@gmail.com>

book/src/lighthouse-ui.md

@@ -0,0 +1,33 @@
+# Lighthouse UI (Siren)
+
+_Documentation for Siren users and developers._
+
+[![Chat Badge]][Chat Link]
+
+[Chat Badge]: https://img.shields.io/badge/chat-discord-%237289da
+[Chat Link]: https://discord.gg/cyAszAh
+
+![ui-overview](./imgs/ui.png)
+
+Siren is a user interface built for Lighthouse that connects to a Lighthouse Beacon Node and
+a Lighthouse Validator Client to monitor performance and display key validator
+metrics. 
+
+The UI is currently in active development. Its resides in the
+[Siren](https://github.com/sigp/siren) repository.
+
+## Topics
+
+See the following Siren specific topics for more context-specific
+information:
+
+- [Installation Guide](./ui-installation.md) - Information to install and run the Lighthouse UI.
+- [Configuration Guide](./ui-configuration.md) - Explanation of how to setup
+	and configure Siren.
+- [Usage](./ui-usage.md) - Details various Siren components. 
+- [FAQs](./ui-faqs.md) - Frequently Asked Questions.
+
+## Contributing
+
+If you find and issue or bug or would otherwise like to help out with the
+development of the Siren project, please submit issues and PRs to the [Siren](https://github.com/sigp/siren) repository.