Tweak migration guide
Tweak migration guide

Co-authored-by: Olivier Halligon <77cccf0d7a72ee0036f6f1a239d5c47ee8799014@halligon.net>
AliSoftware/SwiftGen,SwiftGen/SwiftGen,SwiftGen/SwiftGen,AliSoftware/SwiftGen,AliSoftware/SwiftGen