docs(options): options of node-notifier

Author: Gvozd

README.md

@@ -54,6 +54,15 @@ var config = module.exports = {
 
 ## Configuration
 
+### All `node-notifier` options
+
+You can use any [node-notifier](https://www.npmjs.com/package/node-notifier) options (depending on your OS)
+Except for options generated by the plugin itself:
+* `title` - it can be not only a string, but also a function
+* `message` - generated based on the value of other options
+* `contentImage` - it can be an object with images for different statuses
+* `icon` - matches with `contentImage`
+
 ### Title
 
 Title shown in the notification.