PR template updates

[shakedregev]

Description

Currently we are not prompting developers to test examples manually before submitting PRs. This is not done in the CI pipeline and sometimes results in broken code.

Proposed changes

The template will now remind developers and reviewers to test examples before submitting or approving a PR.

Checklist

Put an x in the boxes that apply. You can also fill these out after creating
the PR. If you're unsure about any of them, don't hesitate to ask. We're here
to help! This is simply a reminder of what we are going to look for before
merging your code.

N/A - documentation only.

• The new code follows Re::Solve style guidelines.
• The new code is documented.
• I have updated CHANGELOG.md to reflect the changes in this PR. If this is a minor PR that is part of a larger fix already included in the file, state so.