mongodb: enable textSearch

I'll see in other answered question that for enable beta feature of textserch in MongoDb i must activate the option in the config file. My question is where and with which command?

That's because i didn't have that parameter in my mongodb.conf file so i suppose i need to add all the line. Which is the correct syntax from these two?

#textSearchEnabled=true

or

#setParameter=textSearchEnabled=true

it's not important where to place the command?

thanks all