Add unsupported help for systemd-resolved (#21922)

source/more-info/unsupported/systemd_resolved.markdown

@@ -0,0 +1,20 @@
+---
+title: "Systemd-Resolved"
+description: "More information on why systemd-resolved marks the installation as unsupported."
+---
+
+## The issue
+
+systemd-resolved is used over D-Bus to resolve DNS queries made by Home Assistant, Supervisor,
+and add-ons. Without it, DNS will not work correctly in your installation.
+
+## The solution
+
+If you see a message about an issue with D-Bus, [resolve that first](/more-info/unsupported/dbus#the-solution).
+
+If the systemd-resolved service is not running or disabled, enable and start it.
+
+If that does not help, reboot your operating system.
+
+As a last resort, you need to reinstall the host running the Supervisor
+with one of the supported operating systems, [see instructions here](/more-info/unsupported/os).