jQuery Grid Plugin - jqGrid

Hi! I'm not american, so excuse me for the syntax...I have a problem: I don' t understand how to insert data in my grid:

I have a php program; when I call it, it send me a json file, in string format, with a ECHO.

I don't understand how I can set parameters of JSONREADER function of jqgrid..

The grid apperas in html page, but it's empty.

I post the code:

PHP:

<?php
$jsstring= '{
        "shops":{
        
        "shop1":{
            "name": "Market FK",
            "address": "Farini street",
            "num": "92838390"
        },
        
        "shop2":{
            "name": "Fruit Yeah",
            "address": "Plaza Tree",
            "num": "4434886"
        }
                }
}';
echo $jsstring;    ?>

THIS JSON FILE IS NOT AN ARRAY. I DON'T KNOW IF AN ARRAY JSON FILE IS BETTER, BUT I CAN'T CHANGE THE JSON FILE!!!

JAVASCRIPT:

$(document).ready(function() {    
$("#id_table ").jqGrid({         url:"url of php file",
                            datatype: "jsonstring",   //is it correct??
                            mtype: "GET",
                            colNames:["Name","Address", "Tel number"],
                            colModel:[     {name:'name',index:'name', width:100}, //is it correct??
                                        {name:'address',index:'address', width:120},
                                        {name:'tel',index:'tel', width:100}
                                        ],
                            jsonReader : {
                                 HERE I DON'T KNOW HOW TO SET
                                  }
                            });     
});

I WANT TO HAVE A GRID WITH:

first column: the names of the shop

second column: the address

third colum: tel numbers

So a grid like this:

• Market FK               Farini street            92838390
• Fruit Yeah               Plaza Tree               4434886

THANK YOU VERY MUCH