In order to publish a Writing NFT with a custom cover image, please follow the steps below:
1. After editing your entry, hit Publish to open up the publishing modal
2. Click "Customize" to change the NFT image
3. Choose or drag and drop an image to use as your NFT image
4. After uploading the custom cover image hit "Sign and Publish"
5. Once you've finished publishing, you'll see the entry published with the NFT cover image