Merge branch 'docs-update-scss-style-guide-tailwind' into 'master'

Update SCSS docs to add information about Tailwind migration

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/142471



Merged-by: Paul Gascou-Vaillancourt <pgascouvaillancourt@gitlab.com>
Approved-by: Paul Gascou-Vaillancourt <pgascouvaillancourt@gitlab.com>
Approved-by: Savas Vedova <svedova@gitlab.com>
Reviewed-by: Paul Gascou-Vaillancourt <pgascouvaillancourt@gitlab.com>
Co-authored-by: Peter Hegman <phegman@gitlab.com>