docs(README): npm link instructions

[wesleyboar]

Overview

Improve/Fix NPM link instructions.

0. Current commands listed are not working and are not what I use successfully.
   • I always add --save-dev to the npm link command and remember not to commit the package.json change.
1. Core-Styles has recently moved to a new repo.
2. I found https://hirok.io/posts/avoid-npm-link, which suggests npx link.

Related

None

Changes

• Reduced npm link instructions.
• Replaced npm link with npx link.

Testing

Run these commands (change path-to/core-styles). Expect no errors.

npm ci
npx link path-to/core-styles # e.g. npx link ../tup-ui/libs/core-styles
npm run build

Notes

This does not fix all problems, like "de-duping", but it's better than what was in here.