minor consistency updates to the writing checklist

[nsryan2]

Summary of changes

This PR makes the grammar employed in the guide consistent:

1. Add periods to the end of each check mark.
2. Make the use of quotes consistent.
3. Make the voice more consistent.
4. Capitalize where appropriate.
5. Fix the spacing in / examples.

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [x] I have read the CONTRIBUTING document.
• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [x] I have updated the documentation accordingly.
• [ ] I have added tests to cover my changes.
• [ ] All new and existing tests passed.

Associated Issues and PRs

• Issue: #

Associated Developers

• Dev: @

Checklist for Reviewers

Reviewers should use this link to get to the Review Checklist before they begin their review.

[smpark7]

If any of the undergrads also want to review this PR, feel free to do so. "The more the merrier" applies for PR reviews.

[nsryan2]

Thanks for the feedback! I addressed all your comments except for the one about e.g., I wasn't sure what that one was about.

[smpark7]

Merging this because I see no other review activity.