1. Go to your Tumblr Customize Page

     

  2. On the left side, look to where it says "Description"

    You probably have some text here already. That's OK.

    Just paste the code After any other text in your description

     

  3. How the cloud appears will depend on your Tumblr Theme.

    Here's an example with the default theme:

    Here's an example with the Effector Theme

    Here's an example with the Munich Theme