Updated Highlight export (markdown)

Highlight-export.md

@@ -1,3 +1,7 @@
 The bundled highlight export plugin is able to export [highlights](https://github.com/koreader/koreader/wiki/Clipboard) and notes added from both native reader in Kindle and the Koreader itself to [Joplin](https://joplinapp.org) as well as local JSON, HTML, or TXT files. [Readwise](https://readwise.io) support is coming soon.
 
-This plugin replaces the deprecated [Evernote export](https://github.com/koreader/koreader/wiki/Evernote-export).
+This plugin replaces the deprecated [Evernote export](https://github.com/koreader/koreader/wiki/Evernote-export).
+
+### Readwise Authorization Token
+
+Get your Readwise authorization token from here: https://readwise.io/access_token