Add Migration Guide

Migration Guide/iZettle SDK 2.0 Migration Guide.md

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+# iZettle SDK v2.0 migration guide
+
+iZettle SDK 2.0 is latest major release containing support for iZettle Reader 2. This guide is provided in order to ease the transition of existing applications using iZettle SDK 1.0+ to the latest release.
+
+## Linking with new framework
+
+iZettle SDK v2.0 introduces a new `iZettleTransport` framework. This framework needs to be linked along current frameworks (`iZettleSDK`, `iZettleShared`, and `iZettlePayments`) in order to work. More info on installation can be found [here](https://github.com/iZettle/sdk-ios#installation).
+
+## Using BLE technology in background modes
+
+The new iZettle Reader 2 uses BLE technology to communicate with the SDK. To make sure that apps using SDK can communicate and work with the new readers in background, you need to enable **Use BLE accessories** in Background Modes in Xcode capabilities. 
+
+You can also do this step manually, and make the change directly in your apps `Info.plist` file. The `UIBackgroundModes` values should look like this:
+
+```
+<key>UIBackgroundModes</key>
+	<array>
+		<string>bluetooth-central</string>
+		<string>external-accessory</string>
+	</array>
+```
+