update readme to include env vars

[kramduckner]

Pull Request Template

Issue Overview

This PR addresses #issue

• This change addresses the issue in full
• This change addresses only certain aspects of the issue
• This change is a dependency for another issue
• This change has a dependency from another issue

Description

Please include a summary of the change and which issue(s) is addressed. Please also include relevant motivation and context. List any dependencies that are required for this change.

How Can This Be Tested/Reviewed?

Provide instructions so we can review.

Describe the tests that you ran to verify your changes. Please also list any relevant details for your test configuration.

Checklist:

• My code follows the style guidelines of this project
• I have added QA notes to the issue with applicable URLs
• I have performed a self-review of my own code
• I have reviewed the changes in a desktop view
• I have reviewed the changes in a mobile view
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have assigned reviewers
• My commit message(s) is/are polished, and any breaking changes are indicated in the message and are well-described

Reviewer Notes:

Steps to review a PR:

• Read and understand the issue, and ensure the author has added QA notes
• Review the code itself from a style point of view
• Pull the changes down locally and test that the acceptance criteria is met
• Also review the acceptance criteria on the Netlify deploy preview (noting that these do not yet include any backend changes made in the PR)
• Either explicitly ask a clarifying question, request changes, or approve the PR if there are small remaining changes but the PR is otherwise good to go

On Merge:

If you have one commit and message, squash. If you need each message to be applied, rebase and merge.