Fixes wrong import path in page customize with sass-cli #3489

[kauefr]

This is a documentation fix. Fixes #3489

Proposed solution

Two changes:

1. Fix bulma folder path for unzipped releases, adding the intermediate /bulma folder
2. Replace hardcoded paths in docs\_includes\steps\add-custom-styles.html with a variable "path" and a for loop. Pages with-webpack.html and with-node-sass.html pages assign path to ../node_modules/bulma and page with-sass-cli.html sets it to ../bulma-{version}/bulma

Tradeoffs

The for loop adds a tiny bit of complexity.

Testing Done

None.

Changelog updated?

No.