Roundcube addressbook is integrated with Epesi contacts and companies. It's readonly with one exception - you can add contact to epesi with plus sign next to email address in message view, so you can add contact & archive message.
Integration doesn't assume that you can import contacts in roundcube... So it's a bug that there is such possibility.
To import you can use Premium/Import module - it can import from csv and xls.
To convert from vcf to csv you can use: http://labs.brotherli.ch/vcfconvert/