docs: Expose telemetry backend requirements in readme (#411)

Maybe formalize some of this in extras requirements later for better
version management.

edx_django_utils/monitoring/README.rst

@@ -41,6 +41,23 @@ Feature support matrix for built-in telemetry backends:
      - ❌
      - ❌
 
+Additional requirements for using these backends:
+
+- ``edx_django_utils.monitoring.NewRelicBackend``:
+
+  - Install the ``newrelic`` Python package
+  - Initialize newrelic, either via the ``newrelic-admin run-program`` wrapper or ``newrelic.agent`` API calls during server startup
+
+- ``edx_django_utils.monitoring.OpenTelemetryBackend``:
+
+  - Install the ``opentelemetry-api`` Python package
+  - Initialize opentelemetry, either via the ``opentelemetry-instrument`` wrapper or ``opentelemetry.instrumentation`` API calls during server startup
+
+- ``edx_django_utils.monitoring.DatadogBackend``:
+
+  - Install the ``ddtrace`` Python package
+  - Initialize ddtrace, either via the ``ddtrace-run`` wrapper or ``ddtrace.auto`` API calls during server startup
+
 Using Custom Attributes
 -----------------------
 

edx_django_utils/monitoring/internal/backends.py

@@ -55,7 +55,7 @@ class NewRelicBackend(TelemetryBackend):
     """
     Send telemetry to New Relic.
 
-    https://docs.newrelic.com/docs/apm/agents/python-agent/python-agent-api/guide-using-python-agent-api/
+    API reference: https://docs.newrelic.com/docs/apm/agents/python-agent/python-agent-api/guide-using-python-agent-api/
     """
     def __init__(self):
         if newrelic is None:
@@ -82,11 +82,6 @@ class OpenTelemetryBackend(TelemetryBackend):
     """
     Send telemetry via OpenTelemetry.
 
-    Requirements to use:
-
-    - Install `opentelemetry-api` Python package
-    - Configure and initialize OpenTelemetry
-
     API reference: https://opentelemetry-python.readthedocs.io/en/latest/
     """
     # pylint: disable=import-outside-toplevel
@@ -108,11 +103,6 @@ class DatadogBackend(TelemetryBackend):
     """
     Send telemetry to Datadog via ddtrace.
 
-    Requirements to use:
-
-    - Install `ddtrace` Python package
-    - Initialize ddtrace, either via ddtrace-run or ddtrace.auto
-
     API reference: https://ddtrace.readthedocs.io/en/stable/api.html
     """
     # pylint: disable=import-outside-toplevel