Restore Buffer polyfill to support e1032d9

Revert "Issue #345: Remove unnecessary polyfill."

This reverts commit 99930b5.

README.md

@@ -207,7 +207,7 @@ You can find an example implementation of `saveDataToFile()` [in the Webpack exa
 Check out the examples [using Webpack](https://github.com/guigrpa/docx-templates/tree/master/examples/example-webpack) and [using Browserify](https://github.com/guigrpa/docx-templates/tree/master/examples/example-browserify) or you can use the browserified bundle directly as discussed below.
 
 ## Polyfilled browser-ready bundle
-As this library depends on the internal NodeJS modules `vm`, `stream`, `util`, and `events`, your build tools have to polyfill these modules when using the library in the browser. We provide a browser build which includes the required polyfills. Its file size is about 300K uncompressed or 85K / 70K with gzip / brotli compression).
+As this library depends on the internal NodeJS modules `vm`, `stream`, `util`, `events` and the `Buffer` global, your build tools have to polyfill these modules when using the library in the browser. We provide a browser build which includes the required polyfills. Its file size is about 300K uncompressed or 85K / 70K with gzip / brotli compression).
 
 You can import the library directly **as a module** using e.g. the unpkg.com CDN, like below, or you can host the `/lib/browser.js` bundle yourself.
 

src/browser-polyfill.ts

@@ -0,0 +1,4 @@
+// eslint-disable-next-line import/no-extraneous-dependencies
+import { Buffer } from 'buffer/';
+
+(<any>globalThis).Buffer = Buffer;

src/browser.ts

@@ -1 +1,2 @@
+import './browser-polyfill';
 export * from './index';