Update readme for v1

readme.md

-First module for docxtemplater.
+The v1 has added two mandatory arguments: `opts.getImage` and `opts.getSize`. See Usage (v1)
 
 [![Build Status](https://travis-ci.org/open-xml-templating/docxtemplater-image-module.svg?branch=master&style=flat)](https://travis-ci.org/open-xml-templating/docxtemplater-image-module)
 [![Download count](http://img.shields.io/npm/dm/docxtemplater-image-module.svg?style=flat)](https://www.npmjs.org/package/docxtemplater-image-module)
@@ -11,13 +11,21 @@ You will need docxtemplater v1: `npm install docxtemplater`
 
 install this module: `npm install docxtemplater-image-module`
 
-# Usage
+# Usage (v1)
 
 Your docx should contain the text: `{%image}`
 
     ImageModule=require(‘docxtemplater-image-module’)
 
     imageModule=new ImageModule({centered:false})
+    opts = {}
+    opts.getImage=function(tagValue) {
+        return fs.readFileSync(tagValue,'binary');
+    }
+
+    opts.getSize=function(img,tagValue) {
+        return [150,150];
+    }
 
     docx=new DocxGen()
         .attachModule(imageModule)
@@ -31,25 +39,38 @@ Your docx should contain the text: `{%image}`
 
     fs.writeFile("test.docx",buffer);
 
-# Options
 
- You can center the images using new ImageModule({centered:true}) instead
+To understand what `img` and `tagValue` mean, lets take an example :
 
-## Size
+If your template is :
+
+    {%myImage}
+
+    and your data:
+
+    {
+        "myImage":'sampleImage.png'
+    }
+
+    tagValue will be equal to "sampleImage.png" , and img will be what ever the getImage function returned
 
-You can set the size of the image to what ever you want in pixel. By default it will be 150x150.
 One of the most useful cases of this is to set the images to be the size of that image.
 
 For this, you will need to install the [npm package ‘image-size’](https://www.npmjs.com/package/image-size)
 then, write:
 
-    imageModule=new ImageModule({centered:false})
-    imageModule.getSizeFromData=function(imgData) {
+    opts = {centered:false}
+    opts.getImage=function(img) {
        sizeOf=require('image-size');
-       sizeObj=sizeOf(imgData);
+       sizeObj=sizeOf(img);
        console.log(sizeObj);
        return [sizeObj.width,sizeObj.height];
     }
+    imageModule=new ImageModule(opts)
+
+# Centering images
+
+ You can center the images using new ImageModule({centered:true}) instead
 
 # Notice