Add Supervisor unsupported system architecture info

source/more-info/unsupported/system_architecture.markdown

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+---
+title: "System architecture"
+description: "More information on why System Architecture marks the installation as unsupported."
+---
+
+## The issue
+
+Supervisor considers `i386`, `armhf`, and `armv7` (all 32-bit system architectures)
+as unsupported. Home Assistant announced the sunset of these architectures in May 2025
+(see [this blog post for more information](https://www.home-assistant.io/blog/2025/05/22/deprecating-core-and-supervised-installation-methods-and-32-bit-systems/)).
+On these system architectures, the Supervisor stops refreshing its update
+information. This means you will no longer receive updates for any component,
+including Home Assistant Core or Add-on updates.
+
+## The solution
+
+You can continue to use the system as is, but it is recommended to move your
+Home Assistant installation onto supported hardware. This makes sure that you'll
+continue to receive software updates, including security updates.
+
+1. To migrate to a supported architecture, [create a full backup](/common-tasks/general/#backups)
+and download it.
+2. Install Home Assistant OS on supported 64-bit hardware. 
+   - Use the [restore from backup feature during onboarding](https://www.home-assistant.io/getting-started/onboarding/) (Option 2).
+   - If you use a Raspberry Pi 3 or Raspberry Pi 4, you can install the 64-bit variants
+of Home Assistant OS. 
+      - See the [Raspberry Pi installation documentation](https://www.home-assistant.io/installation/raspberrypi/) for detailed instructions.