Currently the extension inserts a button in all posts to read the wungle text and highlights those where there is wungle text to be read. To encode text to wungle text, click on the Wungle Text for Tumblr icon in the extensions toolbar. Automatic insertion of the wungle text is hopefully coming soon.
To contribute go to the GitHub and if you have any issues or suggestions file an issue. If you have no idea how to use github but still have a problem send an email to the support email luka.djo(at)onmail.com
