docs(tvix/eval): clarify difference between ThunkSet and Blackhole r/7174

The comment explaining ThunkSet makes it seem like it does the same
think as ThunkRepr::Blackhole.  In fact neither one is a substitute
for the other.  Let's explain the difference.

Change-Id: I89ceaaa9d3c499edbc7d48f70ca5d11f97666c43
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10250
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>
Autosubmit: Adam Joseph <adam@westernsemico.com>

0 files changed, 0 insertions, 0 deletions