You can embed your charts directly in your Medium-post.
To do that, go to Datawrapper, create a chart and then click on "Embed chart on website".
Now, Datawrapper creates a public copy of your chart that you can use. If you make a change to your chart after publishing it, you need to re-publish it so the changes go live. It can take up to a minute for your chart to export:
When your chart is fully exported, Datawrapper will show you the available embed codes for your chart:
In order to embed your chart on Medium.com, you need to copy & paste the direct link to your chart. That is the first blue right below the headline. In this case, it's '//datawrapper.dwcdn.net/BzNXL/1/'.
In your Medium post, start by adding a new paragraph. Then, click the Insert-button, and pick the third option from the left ("Embed"). Enter the URL you've copied from Datawrapper and press enter.
That's all there is to do!
Note: In case your chart does not appear immediately, try pre-pending the link you've copied with "https:", turning "//datawrapper.dwcdn.net/BzNXL/1/" into "https://datawrapper.dwcdn.net/BzNXL/1/".