Add documentation for testing and CI

[cgewecke]

Description

Addresses #3528.

• Adds some description of what tests we have and their intent.
• Adds a link to the browser visual inspection test in the PR template

Human-readable-version

Draft...would love feedback about stuff to add or clarify.

(Have organized this as table which might not really be the right format, idk)

Fixes #3528

Type of change

• Documentation

Checklist:

• I have selected the correct base branch.
• I have performed a self-review of my own code.
• I have updated the CHANGELOG.md file in the root folder.

[coveralls]

Coverage remained the same at 89.638% when pulling 0460c18 on issue/3528 into 5829347 on 1.x.

[ryanio]

cool, but might be a little confusing since other PRs can overwrite it at any time. just thinking out loud, i wonder if we could "append" to the index.html in surge, that would be cool to have a running log of successful (or not) results.

[cgewecke]

Yes this would be ideal: e.g sudden.playground.surge.sh/<branch>/<commit>

As I read surge issue 119, there's no built-in support for this per se and we'd need to maintain our own store of previously published pages.

We can definitely highlight the potential overwrite more clearly in the published page though, will amend this PR for that.

[cgewecke]

834cb78

[ryanio]

really great, wish I had this when I started 😄

[ryanio]

looks so great! 🎉