Update Blazor integration docs with the latest method signatures

[tillig]

autofac/Autofac.Extensions.DependencyInjection#69 - Since writing the Blazor integration docs the methods on WebAssemblyHostBuilder have changed. The docs don't appear to be correct anymore and need to be updated, possibly with more robust/better examples and/or an explanation about how the methods have changed over time to help folks migrating.

I'm not personally a Blazor user - it'd be great to see someone who uses Blazor and the Autofac integration (by way of the standard ASP.NET Core integration points, which is how Autofac integrates) write the docs they'd like to see. Nothing we're doing is "Autofac specific" other than just using the AutofacServiceProviderFactory.