Update readme with link to JavaScript version of template

Author: akrantz

README.md

@@ -2,6 +2,9 @@
 
 This repository contains the source code used by the [Yo Office generator](https://github.com/OfficeDev/generator-office) when you create a new Office Add-in that appears in the task pane. You can also use this repository as a sample to base your own project from if you choose not to use the generator. 
 
+## TypeScript
+This template is written using [TypeScript](http://www.typescriptlang.org/). For the JavaScript version of this template, go to [Excel-Custom-Functions-JS](https://github.com/OfficeDev/Excel-Custom-Functions-JS).
+
 ## Questions and comments
 
 We'd love to get your feedback about this sample. You can send your feedback to us in the *Issues* section of this repository.