Add README to Aspire.Hosting.Azure.AppService

src/Aspire.Hosting.Azure.AppService/README.md

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+# Aspire.Hosting.Azure.AppService library
+
+Provides extension methods and resource definitions for a .NET Aspire AppHost to configure Azure App Service.
+
+## Getting started
+
+### Prerequisites
+
+- Azure subscription - [create one for free](https://azure.microsoft.com/free/)
+
+### Install the package
+
+In your AppHost project, install the .NET Aspire Azure App Service Hosting library with [NuGet](https://www.nuget.org):
+
+```dotnetcli
+dotnet add package Aspire.Hosting.Azure.AppService
+```
+
+## Usage example
+
+In the _AppHost.cs_ file of `AppHost`, add an Azure App Service Environment and publish your project as an Azure App Service website:
+
+```csharp
+var builder = DistributedApplication.CreateBuilder(args);
+
+var appServiceEnvironment = builder.AddAzureAppServiceEnvironment("env");
+
+builder.AddProject<Projects.MyWebApp>("webapp")
+    .WithExternalHttpEndpoints()
+    .PublishAsAzureAppServiceWebsite((infrastructure, site) =>
+    {
+        // Configure the App Service website
+        site.SiteConfig.IsWebSocketsEnabled = true;
+    });
+```
+
+## Azure App Service constraints
+
+When deploying to Azure App Service, the following constraints apply:
+
+- **External endpoints only**: App Service only supports external endpoints. All endpoints must be configured using `WithExternalHttpEndpoints()`.
+- **HTTP/HTTPS only**: Only HTTP and HTTPS endpoints are supported. Other protocols are not supported.
+- **Single endpoint**: App Service supports only a single target port. Resources with multiple external endpoints with different target ports are not supported.
+
+### Publishing compute resources to Azure App Service
+
+The `PublishAsAzureAppServiceWebsite` extension method is used to configure a compute resource (such as a project) to be published as an Azure App Service website when deploying to Azure. This method allows you to customize the App Service website configuration using the Azure Provisioning SDK.
+
+```csharp
+builder.AddProject<Projects.MyApi>("api")
+    .WithHttpEndpoint()
+    .WithExternalHttpEndpoints()
+    .PublishAsAzureAppServiceWebsite((infrastructure, site) =>
+    {
+        // Customize the App Service website settings
+        site.SiteConfig.IsWebSocketsEnabled = true;
+        site.SiteConfig.MinTlsVersion = SupportedTlsVersions.Tls1_2;
+    });
+```
+
+### Adding an Azure App Service Environment
+
+The Azure App Service Environment resource creates the underlying infrastructure needed to host your applications, including:
+
+- An Azure App Service Plan
+- An Azure Container Registry for storing container images
+- A managed identity for accessing the container registry
+- Optionally, the Aspire Dashboard as an Azure App Service website
+
+```csharp
+var appServiceEnvironment = builder.AddAzureAppServiceEnvironment("env");
+```
+
+By default, the Aspire Dashboard is included in the App Service Environment. To disable the dashboard, use the `WithDashboard` extension method:
+
+```csharp
+var appServiceEnvironment = builder.AddAzureAppServiceEnvironment("env")
+    .WithDashboard(enable: false);
+```
+
+## Additional documentation
+
+* https://learn.microsoft.com/azure/app-service/
+* https://github.com/dotnet/aspire/tree/main/src/Components/README.md
+
+## Feedback & contributing
+
+https://github.com/dotnet/aspire