commit-message.txt
Here is my diff: <paste>

Write the commit message.
- A subject line under 72 characters, imperative mood, saying what
  changes and not what file changed.
- A body only if the WHY isn't obvious from the diff. Explain the
  reason and what you considered instead.
- If this diff is really two unrelated changes, say so and tell me
  where to split it.

"Update code" is a message that costs someone twenty minutes later. If the diff does two things, that is the finding, not the message.