Document new options

Author: siphomateke

README.md

@@ -110,6 +110,25 @@ module.exports = {
   }
   ```
 
+- **api** 
+  - Type: `'chrome'|'browser'`
+  - Default: `'browser'`
+  
+  Browser extension API to use.
+
+- **usePolyfill**
+  - Type: `boolean`
+  - Default: `true`
+  
+  Whether to add [webextension-polyfill](https://github.com/mozilla/webextension-polyfill) to polyfill WebExtension APIs in chrome.
+
+- **autoImportPolyfill**
+  - Type: `boolean`
+  - Default: `true`
+
+  Whether to auto import `webextension-polyfill` using Webpack's [ProvidePlugin](https://webpack.js.org/plugins/provide-plugin/).
+
+
 ## Testing
 This library is following the standard styling of vue projects, and those are really the only tests to perform.