The current edition of Warhammer is supported by a number of .pdf FAQ documents published by Games Workshop on their site.
Each update is split into three sections: Errata, Amendments, and ‘Frequently Asked Questions’. The Errata corrects any mistakes in the book, while the Amendments bring the book up to date with the latest version of the rules. The Frequently Asked Questions (or ‘FAQ’) section answers commonly asked questions about the rules. Although you can mark corrections directly in your army book, this is by no means necessary – just keep a copy of the update with your army book.
You can find the these documents here: