[Feature] Clarify that toast Audio doesn't support full C:/ paths

[andrewleader]

Describe the problem this feature would solve

Toasts don't support audio paths that are full paths like C:/... or F:/..., they only support ms-resource and ms-appx. But the comment on AddAudio doesn't explain this, and it doesn't throw an exception either.

Describe the solution

1. Add info to the AddAudio method comment that clarifies what URIs are supported.
2. Throw an exception if an invalid URI is added.

Describe alternatives you've considered

Additional context & Screenshots

[andrewleader]

This would be a good community contribution if anyone wants to take it!