Update Pull Request template (#59062)

# Objective

Give a bit more structure to contributors so that each (potentially new)
contributor doesn't have to come up with their own structure on-the-fly.

## Solution

Update the PR template to include sections for describing

- what the PR is trying to achieve
- how it decided to achieve the goal
- how reviewers can test the work
- demos of the new functionality

## Testing

I used the PR template for this PR, so reviewers can evaluate if they
think the structure is useful.

## Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content adheres to Zed's UI standards
([UX/UI](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
and
[icon](https://github.com/zed-industries/zed/blob/main/crates/icons/README.md)
guidelines)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

## Showcase

<details>
  <summary>Click to view showcase</summary>

### Before

<img width="1082" height="572" alt="image"
src="https://github.com/user-attachments/assets/bc72b8ab-f5ec-4270-b1ec-546456525e92"
/>

### After

<img width="1241" height="945" alt="image"
src="https://github.com/user-attachments/assets/088d90e4-2cb1-42cd-9f8f-0b2783ab7fe4"
/>


</details>

---

Release Notes:

- N/A
c32c037c6bChris Biscardi committed on 6/12/2026, 12:46:42 AM· committed by GitHubparentc486f6f
1 file changedLine totals unavailable