Confusing output; explicitly label legend?

As the second-to-last output, CommonML outputs:

`☑ Rebuild Success ☒ Rebuild Failed ☐ Rebuild Blocked ⋯ Uninteresting`

I kept thinking it was a place holder for the summary (summarizing the build graph above), took me several days of usage before I realized it was the legend for reading the build graph output.

Start by locating the code that produces CommonML's second-to-last build-graph output. Confirm how the checkbox legend is rendered, then make its legend role explicit; done when users can distinguish it from a build summary.

Written by the indexing model from the issue text.