Resources Health Check ReadMe (#4678)

* Resources Health Check ReadMe

* Update src/Libraries/Microsoft.Extensions.Diagnostics.HealthChecks.ResourceUtilization/README.md

Co-authored-by: Sébastien Ros <[email protected]>

---------

Co-authored-by: Sébastien Ros <[email protected]>

Author: Tratcher

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

@@ -1,6 +1,6 @@
 # Microsoft.Extensions.Diagnostics.HealthChecks.ResourceUtilization
 
-Resource utilization health check.
+This provides configurable health check reporting based on the current system resource utilization. See `Microsoft.Extensions.Diagnostics.ResourceMonitoring` for details on how resources are measured. See the [health checks](https://learn.microsoft.com/aspnet/core/host-and-deploy/health-checks) documentation for general usage guidance.
 
 ## Install the package
 
@@ -18,6 +18,50 @@ Or directly in the C# project file:
 </ItemGroup>
 ```
 
+## Usage Example
+
+The health check services can be registered and configured using any of the following API:
+
+```csharp
+public static IHealthChecksBuilder AddResourceUtilizationHealthCheck(this IHealthChecksBuilder builder, params string[] tags)
+public static IHealthChecksBuilder AddResourceUtilizationHealthCheck(this IHealthChecksBuilder builder, IEnumerable<string> tags)
+public static IHealthChecksBuilder AddResourceUtilizationHealthCheck(this IHealthChecksBuilder builder, IConfigurationSection section)
+public static IHealthChecksBuilder AddResourceUtilizationHealthCheck(this IHealthChecksBuilder builder, IConfigurationSection section, params string[] tags)
+public static IHealthChecksBuilder AddResourceUtilizationHealthCheck(this IHealthChecksBuilder builder, IConfigurationSection section, IEnumerable<string> tags)
+public static IHealthChecksBuilder AddResourceUtilizationHealthCheck(this IHealthChecksBuilder builder, Action<ResourceUtilizationHealthCheckOptions> configure)
+public static IHealthChecksBuilder AddResourceUtilizationHealthCheck(this IHealthChecksBuilder builder, Action<ResourceUtilizationHealthCheckOptions> configure, params string[] tags)
+public static IHealthChecksBuilder AddResourceUtilizationHealthCheck(this IHealthChecksBuilder builder, Action<ResourceUtilizationHealthCheckOptions> configure, IEnumerable<string> tags)
+```
+
+For example:
+
+```csharp
+var builder = WebApplication.CreateBuilder(args);
+
+builder.Services.AddHealthChecks()
+    .AddResourceUtilizationHealthCheck(o =>
+    {
+        o.CpuThresholds = new ResourceUsageThresholds
+        {
+            DegradedUtilizationPercentage = 80,
+            UnhealthyUtilizationPercentage = 90,
+        };
+        o.MemoryThresholds = new ResourceUsageThresholds
+        {
+            DegradedUtilizationPercentage = 80,
+            UnhealthyUtilizationPercentage = 90,
+        };
+        o.SamplingWindow = TimeSpan.FromSeconds(5);
+    });
+
+var app = builder.Build();
+
+app.MapHealthChecks("/healthz");
+
+app.Run();
+```
+
+`CpuThresholds` and `MemoryThresholds`'s percentages default to `null` and will not be reported as degraded or unhealthy unless configured. The `SamplingWindow` defaults to 5 seconds.
 
 ## Feedback & Contributing