This plugin add a margin note to your content. For example, if you want to add a source to your post, you can use the shortcode. You will see a margin note in the left of your content when you hover the desired text.
This plugin use the following open source javascript library by Francisco Dans : https://github.com/fdansv/marginotes
If you want to contribute to this plugin, feel free to check the Github repository : https://github.com/Mahjouba91/wp-margin-notes