What document is needed in order for a city to become a incorporated

A city constitution

a city charter from the state legislature

and

to determine how the town will be run for the next year

To incorporate a town, you'll need a lawyer who can handle the paperwork. Once you've decided on where to put your town, the first step toward You-ville is to get a petition signed by some of the people who live there. In Texas, you'll need 10 percent of the voters. In Arkansas, you need to get 75 signatures, no matter how big your town is going to be.