Microsoft.Extensions.Diagnostics.HealthChecks.Common README (#4680)

* add summary information

* Add usage details

* Include AddHealthcChecks() in telemetry publisher example

* Add link to built in metrics doc

src/Libraries/Microsoft.Extensions.Diagnostics.HealthChecks.Common/README.md

@@ -1,6 +1,24 @@
 # Microsoft.Extensions.Diagnostics.HealthChecks.Common
 
-Health check implementations.
+This package contains common health check implementations. Here are the main features it provides:
+
+Application Lifecycle Health Check
+- A provider that's tied to the application's lifecycle based on `IHostApplicationLifetime`
+- Emits unhealthy status when the application is not started, stopping, or stopped
+- Emits healthy status when the application is started and running
+
+Manual Health Check
+- A provider that enables manual control of the application's health
+- Emits unhealthy status when `ReportUnhealthy` is called
+- Emits healthy status when `ReportHealthy` is called
+
+Telemetry Publisher
+- A publisher which emits telemetry (logs and counters) representing the application's health
+- Can be configured to log only when unhealthy reports are received
+
+See the [health checks](https://learn.microsoft.com/aspnet/core/host-and-deploy/health-checks) documentation for general usage guidance.
+
+See the [built in metrics](https://learn.microsoft.com/en-us/dotnet/core/diagnostics/built-in-metrics-diagnostics#meter-microsoftextensionsdiagnosticshealthchecks) page for information regarding the metrics emitted by the telemetry publisher.
 
 ## Install the package
 
@@ -18,6 +36,114 @@ Or directly in the C# project file:
 </ItemGroup>
 ```
 
+## Usage Example
+
+### Application Lifecycle Health Check
+
+The application's lifecycle health check service can be registered and configured using any of the following API:
+
+```csharp
+public static IHealthChecksBuilder AddApplicationLifecycleHealthCheck(this IHealthChecksBuilder builder, params string[] tags)
+public static IHealthChecksBuilder AddApplicationLifecycleHealthCheck(this IHealthChecksBuilder builder, IEnumerable<string> tags)
+```
+
+For example:
+
+```csharp
+var builder = WebApplication.CreateBuilder(args);
+
+builder.Services.AddHealthChecks()
+    .AddApplicationLifecycleHealthCheck();
+
+var app = builder.Build();
+
+app.MapHealthChecks("/healthz");
+
+app.Run();
+```
+
+### Manual Health Check
+
+The manual health check service can be registered and configured using any of the following API:
+
+```csharp
+public static IHealthChecksBuilder AddManualHealthCheck(this IHealthChecksBuilder builder, params string[] tags)
+public static IHealthChecksBuilder AddManualHealthCheck(this IHealthChecksBuilder builder, IEnumerable<string> tags)
+```
+
+Then you can inject `IManualHealthCheck<>` into your services and call the following methods:
+
+```csharp
+public static void ReportHealthy(this IManualHealthCheck manualHealthCheck)
+public static void ReportUnhealthy(this IManualHealthCheck manualHealthCheck, string reason)
+```
+
+For example:
+
+```csharp
+var builder = WebApplication.CreateBuilder(args);
+
+builder.Services.AddHealthChecks()
+    .AddManualHealthCheck();
+
+var app = builder.Build();
+
+app.MapHealthChecks("/healthz");
+
+app.Run();
+
+public class MyService
+{
+    private readonly IManualHealthCheck<MyService> healthCheck;
+
+    // inject IManualHealthCheck<> into your service
+    public MyService(IManualHealthCheck<MyService> healthCheck)
+    {
+        this.healthCheck = healthCheck;
+    }
+
+    public void DoSomething()
+    {
+        // ... do something ...
+
+        if (somethingBadHappened)
+        {
+            this.healthCheck.ReportUnhealthy("reason");
+        }
+
+        this.healthCheck.ReportHealthy();
+    }
+}
+```
+
+### Telemetry Publisher
+
+The telemetry publisher can be registered and configured using any of the following API:
+
+```csharp
+public static IServiceCollection AddTelemetryHealthCheckPublisher(this IServiceCollection services)
+public static IServiceCollection AddTelemetryHealthCheckPublisher(this IServiceCollection services, IConfigurationSection section)
+public static IServiceCollection AddTelemetryHealthCheckPublisher(this IServiceCollection services, Action<TelemetryHealthCheckPublisherOptions> configure)
+```
+
+For example:
+
+```csharp
+var builder = WebApplication.CreateBuilder(args);
+
+// register health check services as needed
+builder.Services.AddHealthChecks()
+    .AddCheck<SampleHealthCheck>("Sample");
+
+// register telemetry publisher
+builder.Services.AddTelemetryHealthCheckPublisher();
+
+var app = builder.Build();
+
+app.MapHealthChecks("/healthz");
+
+app.Run();
+```
 
 ## Feedback & Contributing