Add a black border to the QR code

This makes it easier to measure the dimensions when printed on a white
background, e.g., white paper.

Assets/Scenes/ImageTracking/Images/ReferenceImageLibrary.asset

     m_SerializedTextureGuid:
       m_GuidLow: 288924497207985411
       m_GuidHigh: 4143232447317295274
-    m_Size: {x: 0.05, y: 0.05}
+    m_Size: {x: 0.104775, y: 0.104775}
     m_SpecifySize: 1
     m_Name: QRCode
     m_Texture: {fileID: 2800000, guid: a6fd8503774c0402aa403884f5b77f39, type: 3}