docs: Replace some mentions of jj co with jj new.
#1167
| Job | Run time |
|---|---|
| 6m 3s | |
| 6m 25s | |
| 12m 28s |
jj co with jj new.
#1167
| Job | Run time |
|---|---|
| 6m 3s | |
| 6m 25s | |
| 12m 28s |