Use "image" instead of "container image"

[joelnitta]

Although it seems that the official docs do use container image, this term can be confusing for learners, who often struggle to understand the difference between containers and (container, ahem) images anyways. Furthermore, I have never encountered the term "container image" outside of the official docs or this lesson; everyone else uses "container" or "image". So learners may be confused by that as well when they read other resources about Docker.

[aturner-epcc]

When teaching, I comment explicitly on this point (and this is mentioned in the lesson). I also slip up when talking about "images" during teaching the lesson. I think that the written lesson should follow the official syntax "container image" but the trainer models real life by sometimes using "image" interchangeably.