feat: npm watch synced with live-refresh demo

[wesleyboar]

Overview

Re-build stylesheets on source file change, and—afterward—trigger demo server auto-refresh.

Related

N/A

Changes

• .gitignore the new utility file
• document how to preview build server and preview dev server
• install and configure npm watch
• configure live-refresh after auto-rebuild

Testing

Have two terminals, one code editor, and one browser all visible at once.

1. (terminal A) npm ci
2. (terminal A) npm start
3. (browser) View any pattern.
4. (terminal B) npm run watch
5. (code editor) Change source CSS file of pattern you are viewing such that visual will dramatically change.
6. (browser) Watch page auto-refresh one time—expect no change.
7. (browser) Watch page auto-refresh second time—expect dramatic change.

UI

Skipped.

I am lazy. I don't want to re-arrange all my screens to one window to prove this works to just me, who is the only one looking at these PR's right now.