docs: snippets to add custom ResourceDetector

docs/resources/README.md

@@ -13,4 +13,91 @@ Custom resource detectors can be implemented:
   [OpenTelemetry](../../src/OpenTelemetry/README.md) package), and implement
   the `Detect` method.
 
-A demo ResourceDetector is shown [here](../trace/extending-the-sdk/MyResourceDetector.cs).
+A demo `ResourceDetector` is shown [here](../trace/extending-the-sdk/MyResourceDetector.cs):
+
+```csharp
+using OpenTelemetry.Resources;
+
+internal class MyResourceDetector : IResourceDetector
+{
+    public Resource Detect()
+    {
+        var attributes = new List<KeyValuePair<string, object>>
+        {
+            new KeyValuePair<string, object>("key", "val"),
+        };
+
+        return new Resource(attributes);
+    }
+}
+```
+
+There are two different ways to add the custom `ResourceDetector` to the OTEL signals, via the `Sdk.Create` approach:
+
+```csharp
+using System.Diagnostics;
+using System.Diagnostics.Metrics;
+using Microsoft.Extensions.Logging;
+using OpenTelemetry;
+using OpenTelemetry.Metrics;
+using OpenTelemetry.Resources;
+using OpenTelemetry.Trace;
+
+namespace ExtendingTheSdk;
+
+public class Program
+{
+    private static readonly ActivitySource DemoSource = new("OTel.Demo");
+    private static readonly Meter meterDemoSource = new("OTel.Demo");
+
+    public static void Main()
+    {
+        using var tracerProvider = Sdk.CreateTracerProviderBuilder()
+            .AddSource("OTel.Demo")
+            .SetResourceBuilder(ResourceBuilder.CreateEmpty().AddDetector(new MyResourceDetector()))
+            .Build();
+
+        using var meterProvider = Sdk.CreateMeterProviderBuilder()
+            .SetResourceBuilder(ResourceBuilder.CreateEmpty().AddDetector(new MyResourceDetector()))
+            .Build();
+
+        using var loggerFactory = LoggerFactory.Create(builder =>
+        {
+            builder.AddOpenTelemetry(options =>
+            {
+                options.SetResourceBuilder(ResourceBuilder.CreateDefault().AddDetector(
+                    new MyResourceDetector()));
+            });
+        });
+
+        using (var foo = DemoSource.StartActivity("Foo"))
+        {
+            using (var bar = DemoSource.StartActivity("Bar"))
+            {
+                using (var baz = DemoSource.StartActivity("Baz"))
+                {
+                }
+            }
+        }
+
+        var counter = MeterDemoSource.CreateCounter<long>("counter");
+        for (var i = 0; i < 20000; i++)
+            counter.Add(1, new("tag1", "value1"), new("tag2", "value2"));
+
+        var logger = loggerFactory.CreateLogger("OTel.Demo");
+        logger.LogInformation("Hello from {name} {price}.", "tomato", 2.99);
+    }
+}
+```
+
+or via `OpenTelemetry.Extensions.Hosting` method:
+
+```csharp
+    services.AddSingleton<MyResourceDetector>();
+
+    services.AddOpenTelemetry()
+        .ConfigureResource(builder =>
+            builder.AddDetector(sp => sp.GetRequiredService<MyResourceDetector>()))
+        .WithTracing(builder => builder.AddConsoleExporter())
+        .WithMetrics(builder => builder.AddConsoleExporter());
+```