Clarify simple linear dag

[kyprifog]

A simple linear dag has a slightly confusing output like this:

step_1
step_2
step_3
step_4

Which maybe someone wouldn't realize is a dag at first glance (without context). I thought maybe it would be nice to have pipes to indicate that there is still a transition like:

step_1
|
step_2
|
step_3
|
step_4

I started to look into this change, but I thought that maybe this was inconsistent with the goal of reaching 1-1 parity with the git dag output. If so feel go ahead and close this one.