Continue structural port from Spring Boot to Undertow

- Configuration options
- Configuration documentation

docs/README.md

@@ -5,6 +5,7 @@
 - Installation
   - [Debian package](install/debian.md)
   - [ArchLinux](install/archlinux.md)
+  - [NixOS](install/nixos.md)
   - [Docker](install/docker.md)
   - [From source](install/source.md)
 - [Architecture overview](architecture.md)
@@ -22,4 +23,4 @@
     - [SendGrid](threepids/notification/sendgrid-handler.md)
 - [Sessions](threepids/session/session.md)
   - [Views](threepids/session/session-views.md)
-- [FAQ](faq.md)
+- [FAQ](faq.md)