That secondary weapon is that the handgun or do you mean i from the start of the game can have a eg. machinegun and bow? I know i can unlock more holsters from the perk tree, but i understood you start the game with 2 holdsters + the handgun holster.
You have to play a huge portion of the game before U can carry more weapons. So either U have to devote to a stealth weapon like a bow or loud like a automatic rifle for most of the game. Which is a real shame, to be locked into one playstyle like that.