Provide Microsoft.AspNetCore.Components.WebAssembly package README (dotnet#57773)

Author: MackinnonBuck

src/Components/WebAssembly/WebAssembly/src/PACKAGE.md

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+## About
+
+`Microsoft.AspNetCore.Components.WebAssembly` provides support for building client-side single-page applications (SPAs) with Blazor running under WebAssembly.
+
+## How to Use
+
+To get started with Blazor, see the [official documentation](https://learn.microsoft.com/aspnet/core/blazor).
+
+## Feedback & Contributing
+
+`Microsoft.AspNetCore.Components.WebAssembly` is released as open-source under the [MIT license](https://licenses.nuget.org/MIT). Bug reports and contributions are welcome at [the GitHub repository](https://github.com/dotnet/aspnetcore).