README.md: Mention that xemu-dashboard is a free replacement for the official proprietary Xbox dashboard

[davidhedlund]

It would be beneficial to mention that this in the xemu-dashboard README:

The xemu-dashboard is free under the MIT license. In contrast, the official Xbox dashboard is proprietary and controlled by Microsoft.

[mborgerson]

The "copyright free" claim of the xemu-hdd-image README referred to the formatted HDD image. The claim does not really work here, because the dashboard being distributed is Copyright (c) 2025 Ryzee119. Though we should probably mention that it is not affiliated in any way with the official Microsoft Xbox dashboard