docs: add troubleshooting section (#1800)

* add troubleshooting section

* add no traces and support section

* fix typo

Author: Kyle-Verhoog

docs/index.rst

@@ -163,3 +163,4 @@ Indices and tables
     advanced_usage
     contributing
     release_notes
+    troubleshooting

docs/troubleshooting.rst

@@ -0,0 +1,36 @@
+===============
+Troubleshooting
+===============
+
+Traces not showing up in the app
+================================
+
+The most common reason for traces not being received by Datadog is an agent
+communication issue:
+
+- Ensure the Datadog agent is running and reachable over the network if not on
+  the same host.
+- Ensure that ``ddtrace`` is configured with the hostname and port of the
+  agent. See :ref:`Configuration` for the configuration variables.
+
+To verify that a connection is being made to the agent, enable start-up logs
+with the environment variable ``DD_TRACE_STARTUP_LOGS=true``. A diagnostic log
+that looks like ``DATADOG TRACER DIAGNOSTIC...`` will be displayed with the
+connection error if there is a problem connecting to the agent.
+
+
+Failed to send traces... ``ConnectionRefusedError``
+===================================================
+
+``Failed to send traces to Datadog Agent...: ConnectionRefusedError(111, 'Connection refused')``
+
+The Datadog Agent has a limit to the number of connections it can receive. This
+can be configured with the instructions here: https://docs.datadoghq.com/tracing/troubleshooting/agent_rate_limits/#max-connection-limit.
+
+
+Still having issues?
+====================
+
+If none of the above was able to resolve the issue then please reach out to
+Datadog support at [email protected]. Or view the other support options
+listed here: https://www.datadoghq.com/support/.