func (s *UsersService) PromoteSiteAdmin(ctx context.Context, user string) (*Response, error) {
	u := fmt.Sprintf("users/%v/site_admin", user)
	req, err := s.client.NewRequest("PUT", u, nil)
	if err != nil {
		return nil, err
	}
	return s.client.Do(ctx, req, nil)
}
PromoteSiteAdmin promotes a user to a site administrator of a GitHub Enterprise instance.

GitHub API docs: https://developer.github.com/v3/users/administration/#promote-an-ordinary-user-to-a-site-administrator
package github
import (
	"context"
	"fmt"
)