Hi there, this project is great but I'm having trouble getting a working setup involving an asset catalog when my defaultSourceDirectoryType is syncedFolder.

Steps to reproduce:

1. Download and unpack my sample project: Example.zip
2. Run xcodegen generate from the root
3. Open up the xcodeproj and run it
4. The example app is supposed to render an image (the XcodeGen logo), but it will fail to find it in the asset catalog

You can see that there is no build phase that will copy the asset catalog.
If I manually add it in Xcode, then everything is fine.

In my project.yml file you can see I have added a commented-out extra source path to try and explicitly add the asset catalog.
What's interesting is that if you uncomment and generate, the following will happen:

• The copy bundle resources phase is added by XcodeGen this time
• The asset catalog will appear in the copy list twice!
• The copy list will also include the info.plist, which causes a build failure ("Multiple commands produce .../Info.plist")

Deleting the line defaultSourceDirectoryType: syncedFolder will solve the issue, but I want to use syncedFolder because otherwise I have to keep running the generator whenever I add files. Unless I'm misunderstanding something about how you express the target sources?

Thanks!