You don't have to set EAN13 code in settings ? Once you do it Link should be added to the main product page.

Settings/Companies/YourCompany/Configuration/ at the bottom of the window should be EAN company code, 

EDIT

Create name for this code, provide all required details and voila :)

SAVE

go to the product page and it should be displayed somwhere near the field EAN Code

It is very good idea to install ProductBarcodeGenerator ;)

https://www.odoo.com/apps/modules/8.0/product_barcode_generator/