Feed strings into RapidJson to output JSON

I'm looking at using RapidJSON to convert some data strings to json format. This is what I have as my starting point.

#include "rapidjson/writer.h"
#include "rapidjson/stringbuffer.h"
#include <iostream>

using namespace rapidjson;
using namespace std;

std::string item_name
std::string item_address

itemname = "John";
item_address = "New York";

int main() {
 StringBuffer s;
 writer<StringBuffer> writer(s);

 writer.StartObject();
 writer.String("hello");
 writer.EndObject();

 std:cout << s.GetString() <<endl;
 return 0;
 }

The output format would be something like this:

{"item": {"name": "John", "address": "New York"}}

I'm confused about how I am meant to put my string contents into the json, as well as define that it should be a child of "item". Any help would be appreciated.