there's an example.txt file inside the mod just in case. to make settings for your gamemode, you need to put a settings.txt file inside of your gamemode directory.
name NAME OF THE SETTING
variable $VARIABLE::TO_CHANGE
type bool (or string, list, number)
default DEFAULT NUMBER, STRING, OR LIST CHOICE
content (If you choose LIST as the type, make a '|' separated line of options. If you choose NUMBER, then the format goes as: MINIMUM MAXIMUM INCREMENT
separate the individual settings by spaces. here's an example (there can be as many settings as you want):
name Bakery Name
variable $BakeryGamemode::BakeryName
type string
default The Bakery
name Difficulty
variable $BakeryGamemode::Difficulty
type list
default 0
content Easy|Normal|Hard