add hint about Xcode build error

Author: hollance

Diff for: Errata.markdown

@@ -2,4 +2,10 @@
 
 This is a list of known mistakes and bugs in the book *The Complete Beginner's Guide to Audio Plug-in Development* and/or the accompanying source code.
 
-(No issues reported yet. Phew!)
+## Xcode error: A build only device cannot be used to run this target
+
+You may get the following error message from Xcode:
+
+![](Images/BuildOnlyDeviceError.png)
+
+This happens when the run destination at the top of the Xcode window is set to **Any Mac**. When Any Mac is selected, Xcode only lets you build the project but not run it. To fix this, click on Any Mac and change this setting to **My Mac**.