chore!: deprecate datadog exporter

Author: mabdinur

Diff for: exporter/opentelemetry-exporter-datadog/README.rst

@@ -10,6 +10,11 @@ This library allows to export tracing data to `Datadog
 <https://www.datadoghq.com/>`_. OpenTelemetry span event and links are not
 supported.
 
+Deprecated
+------------
+This exporter has been deprecated. To export your OpenTelemetry tracer to datadog please refer to [Datadog Python Open Standards](https://docs.datadoghq.com/tracing/setup_overview/open_standards/python/#opentelemetry).
+
+
 Installation
 ------------
 
@@ -26,4 +31,4 @@ References
 ----------
 
 * `Datadog <https://www.datadoghq.com/>`_
-* `OpenTelemetry Project <https://opentelemetry.io/>`_
+* `OpenTelemetry Project <https://opentelemetry.io/>`_