From your Shopify admin, go to Online Store > Themes.
Click Actions > Edit code.
The code editor shows a directory of theme files on the left, and a space to view and edit the files on the right like the following image:
Select the layout.liquid file (or theme.liquid) to edit the contents of your Shopify website and look for the closing </body> tag. Just before the tag, paste your WebReader script and save the changes.
Your WebReader should now show on your Shopify website. If it doesn't, please contact us.