License for BOOK.md

[donaldr3]

I was checking this package for inclusion in the Free Software Directory and while the documentation is very robust it wasn't clear what license BOOK.md is distributed under. Thank you for clarifying the situation on the document, and let me know when you get to it so I can approve the entry in the directory.

[Iury de oliveira gomes figueiredo]

Well, i would stick with the same license of the package. Thank you for notifyiing me.