Fixing with a nail gun is the best practice. But nail guns aren't cheep. And if you are only using it for one job, it isn't really cost affective. A half decent second hand one will set you back around £150. No more nails or a trade alternative will cost you £2.50 a tube approximately, from a builders merchant and if applied correctly, will hold for years. Alternatively, you could could pin them by hand, but I suggest that if you are not a regular user of a hammer then drill pilot holes through the bead, carefully hammer the nails in until they are stuck out about 5mm and then using a nail punch, tap them home. This will help you prevent any damage to the floor, beading, skirting caused by stray hammer blows and will give you a similar finish to the nail gun method.