fix(client): fix typo in overlay config hint

[davidohlin]

Description

I was trying to disable the overlay by setting hmr.overlay to false in the config as described in the overlay. However, the correct key is server.hmr.overlay. I also phrased it to look more like the description in the docs :-)

Additional context

No!

---

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Before submitting the PR, please make sure you do the following

• Read the Contributing Guidelines.
• Read the Pull Request Guidelines and follow the Commit Convention.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.