docs: update PR template with sandbox info

[FossPrime]

Summary

• [x] If you have not already please refer to the contributing guideline as described here
• [x] Tell us about the problem your pull request is solving.
• [x] Are there any open issues that are related to this? Is this PR dependent on PRs in other repos?
  • If so, please mention them to keep the conversations linked together.
• [x] I'm using https://www.conventionalcommits.org/en/v1.0.0/ for the PR title

Other Information

If there's anything else that's important and relevant to your pull request, mention that information here. This could include benchmarks, or other information.

Your PR will be reviewed by a core team member and they will work with you to get your changes merged in a timely manner. If merged your PR will automatically be added to the changelog in the next release.

If your changes involve documentation updates please mention that and link the appropriate PR in feathers-docs.

To run this pull request in a clean container visit:

1. Visit https://replit.com/new/github/feathersjs/feathers-chat
2. Run git pull origin pull/255/head

Thanks for contributing to Feathers! :heart:

[FossPrime]