This is just a suggestion. I was going to follow this particular lesson when I realized that tileset.png already has the slopes. Perhaps, you could include an unedited version of the tileset with the course files for people who want to follow this lesson.
I just checked the video. If someone wants to draw the tileset from 0, they should be able to do so. If I included the tileset without slopes, it'd just be a document with a rectangle in it, and may confuse people who'll then see two tileset textures in the project.
But thanks for the heads up.