Update manual_instrumentation.md adding .Net entry (#27424)

Co-authored-by: buraizu <bryce.eadie@datadoghq.com>

Author: gitstevenpham

content/en/data_streams/manual_instrumentation.md

@@ -96,6 +96,75 @@ set_consume_checkpoint(
 
 {{< /code-block >}}
 {{% /tab %}}
+{{% tab ".Net" %}}
+The following example propagates the trace context. See [Trace Context Propagation][1] for more information.
+
+<div class="alert alert-warning">
+  <strong>Note:</strong> In async operations, this may not work as expected because the context derived from the incoming message can be lost when producing a new message in different threads.
+</div>
+
+#### Producer configuration
+
+{{< code-block lang="csharp" >}}
+using Datadog.Trace;
+
+using (var scope = Tracer.Instance.StartActive("produce"))
+{
+    var headers = new Headers();
+    var msg = new Message { Value = "<ANY-VALUE>", Headers = headers};
+
+    new SpanContextInjector().InjectIncludingDsm(
+        msg.Headers,
+        SetHeader,
+        scope.Span.Context,
+        messageType: "<DATASTREAM-TYPE>",
+        target: "<QUEUE-OR-TOPIC-NAME>"
+    );
+
+    // Produce the message
+}
+
+// Specific to how the header is modeled
+static void SetHeader(Headers headers, string key, string value)
+{
+    headers.Add(new Header(key, value));
+}
+{{< /code-block >}}
+
+#### Consumer configuration
+
+{{< code-block lang="csharp" >}}
+using Datadog.Trace;
+
+var startTime = DateTimeOffset.UtcNow;
+var msg = consumer.Consume();
+var parentContext = new SpanContextExtractor().ExtractIncludingDsm(
+    msg.Headers,
+    GetHeader,
+    messageType: "<DATASTREAM-TYPE>",
+    source: "<QUEUE-OR-TOPIC-NAME>"
+);
+
+using (var scope = Tracer.Instance.StartActive("consume",
+       new SpanCreationSettings,
+       {
+           Parent = parentContext,
+           StartTime = startTime
+       })
+)
+{
+    // Do something with the message
+}
+
+// Specific to how the header is modeled
+static IEnumerable<string?> GetHeader(Headers headers, string key)
+{
+    yield return header.GetByKey(key);
+}
+{{< /code-block >}}
+
+[1]: /tracing/trace_collection/trace_context_propagation/?tab=net#additional-use-cases
+{{% /tab %}}
 {{< /tabs >}}
 ## Further Reading