Add hints and ebook-links for some challenges (for #305)
Add hints and ebook-links for some challenges
(for #305)

bkimminich/juice-shop,bkimminich/juice-shop,bkimminich/juice-shop,bkimminich/juice-shop,bkimminich/juice-shop,bonze/juice-shop,m4l1c3/juice-shop,bonze/juice-shop,bonze/juice-shop,oviroman/disertatieiap2017,oviroman/disertatieiap2017,bkimminich/juice-shop,bonze/juice-shop,m4l1c3/juice-shop,bonze/juice-shop,oviroman/disertatieiap2017,m4l1c3/juice-shop,m4l1c3/juice-shop,oviroman/disertatieiap2017,m4l1c3/juice-shop,oviroman/disertatieiap2017