Update lockbot comment to encourage linking to issue

[MinchinWeb]

Further to #938.

Should starred/pushpinned issues be immune to being closed? I think that was the purpose of that label.

Also, I think the closing text should encourage people to link back to "this" issue, so the conversation can be followed.

Checklist

• [ n/a ] The code change is tested and works locally.
• [ n/a ] Tests pass. Your PR cannot be merged unless tests pass. --
  poetry run behave
• [ n/a ] The code passes linting via
  black (consistent code styling). --
  poetry run black --check . --verbose --diff
• [ n/a ] The code passes linting via pyflakes
  (logically errors and unused imports). -- poetry run pyflakes jrnl features
• [ n/a ] There is no commented out code in this PR.
• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open
  Pull Requests for the same update/change?
• Have you added an explanation of what your changes do and why you'd like
  us to include them?
• [ n/a ] Have you written new tests for your core changes, as applicable?

[wren]

The lock bot only acts on closed issues, so there's no need to exempt any labels.

I like the addition to the comment, though.

[wren]

To clarify, stalebot closes issues, and lockbot locks commenting after the issue is closed. The entire process takes about 5 months of no activity.

[MinchinWeb]

Ok, this has been slimmed down to the just the comment on linking to the closed issue!