Add spec for instrumenting Azure services

specs/agents/tracing-instrumentation-azure.md

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+## Azure services spans
+
+We describe how to instrument some of Azure's services in this document.
+Some of the services can use existing specs. When there are differences or additions, they have been noted below.
+
+### Azure Service Bus
+
+Azure Service Bus is a message broker service. The [messaging spec](tracing-instrumentation-messaging.md) can 
+be used for instrumenting Azure Service Bus, but the follow specifications supersede those of the messaging spec.
+
+#### Typing
+
+- Spans: 
+  - `span.subtype`: `azureservicebus` 
+
+#### Additional actions
+
+Azure Service Bus supports actions that should be traced in addition to `SEND` and `RECEIVE`:
+
+- `SCHEDULE`
+
+  Message published to the bus, but not visible until some later point.
+
+- `RECEIVEDEFERRED`
+
+  Message received from the bus, but marked as deferred on the bus, then later retrieved with receive deferred.
+
+#### Naming
+
+Messages can be sent to queues and topics, and can be received from queues and topic subscriptions.
+
+Transaction and span names should* follow these patterns:
+
+For send and schedule,
+
+`AzureServiceBus SEND|SCHEDULE to <QUEUE-NAME>|<TOPIC-NAME>`
+
+For receive and receive deferred,
+
+`AzureServiceBus RECEIVE|RECEIVEDEFERRED from <QUEUE-NAME>|<TOPIC-NAME>/Subscriptions/<SUBSCRIPTION-NAME>`