Fix: completed cut-off sentence in contributor docs

[SHAMIKH-ANWAR]

Progress Towards #3596

Changes:

• Completed the cut-off sentence under the "Pull Request Templates" section in preparing_a_pull_request.md.
• Ensured the contributor documentation flows correctly without leaving the section incomplete.

Verification:

• No linting errors (npm run lint)
• No test errors (npm run test)
• Branch is up to date with develop
• Change is documentation-only

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[raclim]

Thanks for giving this a go @SHAMIKH-ANWAR!

I edited the description for this PR to be "Progress Towards" rather than "Fixes", since the "Pull Request Templates" section content is still missing. Since this PR helps tidy up the current state of the doc, I'm going to merge this in!

As a note for future PRs, please aim for issues that have a "Ready for Work" label, or do not have a "Awaiting Maintaner Approval" label before opening one to ensure that the proposed solutions are in the right direction!