Added an express example

README.md

@@ -29,6 +29,9 @@ Manipulate .xlsx files - easy.
  * Support for other spreadsheet cell types (e.g. date, hours, etc.) 
 
 ## TL;DR Simple Usage Examples
+
+### Create a new .xlsx file from scratch
+
 ````javascript
 var fs = require('fs');
 var kexcel = require('kexcel');
@@ -37,4 +40,32 @@ kexcel.new().then(function (wb) {
   sheet.setCellValue(1, 1, 'Hello world!');
   return wb.pipe(fs.createWriteStream('output.xlsx'));
 });
+````
+
+### Modify an existing .xlsx file and send it through a http response (express)
+````javascript
+var path = require('path');
+var express = require('express');
+var app = express();
+var kexcel = require('kexcel');
+
+app.get('/', function (req, res) {
+    kexcel.open(path.join(__dirname, 'example.xlsx')).then(function(workbook) {
+        var sheet = workbook.getSheet(0);
+        sheet.setCellValue(1,1,'Hello World!');
+        sheet.setRow(2, ['Hello', 'even', 'more', 'Worlds']);
+        sheet.setRow(3, [1, '+', 2, 'equals','=A3+C3']);
+
+        res.setHeader('Content-disposition', 'attachment; filename=example.xlsx');
+        res.setHeader('Content-type', 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet');
+        workbook.pipe(res);
+    });
+});
+
+var server = app.listen(3000, function () {
+    var host = server.address().address;
+    var port = server.address().port;
+
+    console.log('KExcel app listening at http://%s:%s', host, port);
+});
 ````