Add Avalonia 11.2 compatibility notification in README

[rabbitism]

[rabbitism]

This issue is caused by 11.2 incompatibility. We either need to bump Ursa version and make it only compatible with 11.2 starting from this new version, or waiting to see if AvaloniaUI/Avalonia#17398 can be merged and we can add a note that Ursa won't work with the specific 11.2.0 version.

[rabbitism]

As Avalonia 17398 is merged and will be shipped with 11.2.1, we only need to add a note that Ursa Timepicker is ONLY not compatible with Avalonia 11.2.0.