make admin user in mongodb code example

Example 1: create admin user in mongodb

use admin
db.createUser(
      {
          user: "username",
          pwd: "password",
          roles: [ "root" ]
      }
  )

Example 2: mongodb add admin user

use admin
db.createUser({
  user: "username",
  pwd: "password",
  roles: [ "root" ]
})