Add PR template

[eyelidlessness]

This is roughly based on the templates from:

• getodk/central
• enketo/enketo

It specifically adds a browser checklist, as that discussion is what prompted us to add this.

---

Before we merge this, I would like to consider adding:

• A section to describe the PR's changes. This is something I'm trying to make an effort to do on at least non-trivial/non-obvious changes, and would like to encourage as it's really helpful to look back and find context for changes as they occur. This could be really basic, or could encourage specific kinds of details (e.g. things to look out for, things that were intentionally deferred, aspects of approach of particular interest/warranting particular scrutiny). If the latter, there may be overlap with the best solution section.
• Either checkboxes for adding/skipping a changeset, or at least a text reminder. I'm hoping this will become more habitual over time, but for now it seems like it might be good to have the extra prompt.

[changeset-bot]

🦋 Changeset detected

Latest commit: e0fba71

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 0 packages

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[sadiqkhoja]

LGTM!

I also like the idea of adding "Changes" section in the PR