Added upgrade instructions

Author: KDederichs

Diff for: UPGRADE.md

@@ -0,0 +1,89 @@
+#Upgrading Enqueue:
+
+From `0.8.x` to `0.9.x`:
+
+##Processor declaration
+
+`Interop\Queue\PsrProcessor` interface has been replaced by `Interop\Queue\Processor`
+`Interop\Queue\PsrMessage` interface has been replaced by `Interop\Queue\Message`
+`Interop\Queue\PsrContext` interface has been replaced by `Interop\Queue\Context`
+
+
+
+##Symfony Bundle
+
+###Configuration changes:
+
+`0.8.x`
+
+
+```
+enqueue:
+    transport:
+       default: ...
+```
+
+`0.9.x`
+
+
+```
+enqueue:
+    default:
+        transport: ...
+```
+
+In `0.9.x` the client name is a root config node.
+
+The `default_processor_queue` Client option was removed.
+
+###Service declarations:
+
+`0.8.x`
+
+
+```
+tags:
+     - { name: 'enqueue.client.processor' }
+```
+
+`0.9.x`
+
+
+```
+tags:
+     - { name: 'enqueue.command_subscriber' }
+     - { name: 'enqueue.topic_subscriber' }
+     - { name: 'enqueue.processor' }
+```
+
+The tag to register message processors has changed and is now split into processor sub types.
+
+###CommandSubscriberInterface `getSubscribedCommand`
+
+
+`0.8.x`
+
+return `aCommandName` or 
+```
+      [
+        'processorName' => 'aCommandName',
+        'queueName' => 'a_client_queue_name',
+        'queueNameHardcoded' => true,
+        'exclusive' => true,
+      ]
+```
+
+`0.9.x`
+
+
+return `aCommandName` or 
+```
+     [
+        'command' => 'aSubscribedCommand',
+        'processor' => 'aProcessorName',
+        'queue' => 'a_client_queue_name',
+        'prefix_queue' => true,
+        'exclusive' => true,
+     ]
+```
+