[Feature Request] Document host builder caveats

[cretz]

Describe the solution you'd like

Look at this snippet:

using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Temporalio.Client;
using Temporalio.Extensions.Hosting;
using Temporalio.Worker;
using Temporalio.Workflows;

async Task RunAsync()
{
    // Start workflow
    var client = await TemporalClient.ConnectAsync(new("localhost:7233"));
    await client.StartWorkflowAsync(
        (MyWorkflow wf) => wf.RunAsync(),
        new(id: $"wf-{Guid.NewGuid()}", "my-task-queue"));

    // Run worker (change to false and this will start working)
    const bool useHostBuilder = true;
    try
    {
        if (useHostBuilder)
        {
            var builder = Host.CreateApplicationBuilder();
            builder.Services.AddHostedTemporalWorker("localhost:7233", "default", "my-task-queue").AddWorkflow<MyWorkflow>();
            var host = builder.Build();
            // Change next line to "await host.RunAsync();" and it will start working
            host.Run();
        }
        else
        {
            var worker = new TemporalWorker(
                client, new TemporalWorkerOptions("my-task-queue").AddWorkflow<MyWorkflow>());
            await worker.ExecuteAsync(default);
        }
    }
    catch (OperationCanceledException)
    {
        Console.WriteLine("Workers cancelled");
    }
}

await RunAsync();

[Workflow]
public class MyWorkflow
{
    [WorkflowRun]
    public Task<string> RunAsync() => Task.FromResult("done");
}

It doesn't poll, but if you change host.Run() to host.RunAsync() it works. Very strange. So document that in the Temporalio.Extensions.Hosting README. Also document the caveat about issue 36063 in https://github.com/dotnet/runtime (not linking by intention) which trips people up and is a known issue.