Findability of detailed JS/CSS installation docs from 'Install from npm'

[hannalaakso]

What

Had feedback from a user who was looking at Install from npm and wanted to find out more about

selectively include the CSS or JavaScript for individual components

but on clicking through to Install with Node.js package manager (npm) couldn't find the more detailed JS/CSS installation instructions.

Why

We should help users to get to the part of the docs that are flagged under Install from npm.

Who needs to know about this

Mark

Further detail

I spoke to @m-green about this briefly who thought that we might want to link through to the specific docs page from the bullet point. For that reason I've created this issue in govuk-design-system but we might decide to fix this in the frontend-docs-repo instead.