Cannot run docker image to activate Wolfram Engine 

Using the prebuilt image, doing `docker run -it myname/wolframengine:1.0` tells me that it's unable to find the image. Below is the error message:

`Error response from daemon: manifest for myname/wolframengine:1.0 not found: manifest unknown: manifest unknown`

I'm following the README file, but perhaps there is a step in between that I'm missing?