adding readme

package.json

@@ -20,8 +20,6 @@
   "author": "Jacob Baring <jacob@dnamicro.com>",
   "dependencies": {
     "bluebird": "^3.5.1",
-    "co": "^4.6.0",
-    "dotenv": "^4.0.0",
     "fs-extra": "^4.0.2",
     "gm": "^1.23.0"
   },

readme.md

@@ -0,0 +1,23 @@
+# PDF2Pic  
+
+Node module for converting PDF to image based on pdf2img by Fitra Adity  
+
+## Usage  
+
+```javascript
+let PDF2Pic = require('pdf2pic')
+let converter = new PDF2Pic({
+    density: 100,
+    savename: "untitled",
+    savedir: "./images"
+})
+
+converter.convert("/path/to/pdf/sample.pdf")
+         .then(resolve => {
+             console.log("image converted successfully")
+         })
+```  
+
+___
+
+This module is based on Fitra Adity's Great work.

src/index.js

@@ -75,6 +75,12 @@ class PDF2IMG {
 
     }
 
+    /**
+     * Intialize converter
+     * @param {String} pdf_path path to file
+     * @param {Page} page page number to be converted (-1 for all pages)
+     * @return {Object} image status
+     */
     async convert(pdf_path, page = 1) {
         this.isValidPDF(pdf_path)
         this.fileExists(pdf_path)