docs: Update documentation comments in FileUpdateTransaction.h

[freya-docs]

Description:

This PR updates documentation comments for clarity in FileUpdateTransaction.h

Related issue(s):

Fixes #1166

[github-actions]

Hi @freya-docs 👋, thank you for submitting this PR!
I'm your PR Helper Bot and I'll be keeping track of your PR's
status to help you get it approved and merged.

This comment will stay updated as you make changes.
Here's where things stand:

---

PR Checks

❌ DCO Sign-off -- The following commits are missing the required DCO sign-off:

• 4392937 Merge branch 'hiero-ledger:main' into improve-doc-clarity

Please add Signed-off-by: Your Name <email> to each commit (e.g. git commit -s). See the Signing Guide.

---

✅ GPG Signature -- All commits have verified GPG signatures.

---

✅ Merge Conflicts -- No merge conflicts detected.

---

✅ Issue Link -- Linked to #1166 (assigned to you).

---

All checks must pass before this PR can be reviewed.

[rwalworth]

Thanks for working on this @freya-docs! The setContents and setFileMemo updates look good. I left a couple of comments below that need to be addressed before we can merge. Let me know if you have any questions!

[rwalworth]

LGTM, thank you @freya-docs! Running the workflows now and will merge once they complete.