add themes

themes/hugo-book/.github/workflows/main.yml

themes/hugo-book/.gitignore

themes/hugo-book/LICENSE

themes/hugo-book/README.md

themes/hugo-book/archetypes/docs.md

themes/hugo-book/archetypes/posts.md

themes/hugo-book/assets/_custom.scss

themes/hugo-book/assets/_defaults.scss

themes/hugo-book/assets/_fonts.scss

themes/hugo-book/assets/_main.scss

themes/hugo-book/assets/_markdown.scss

themes/hugo-book/assets/_print.scss

themes/hugo-book/assets/_shortcodes.scss

themes/hugo-book/assets/_utils.scss

themes/hugo-book/assets/_variables.scss

themes/hugo-book/assets/book.scss

themes/hugo-book/assets/clipboard.js

themes/hugo-book/assets/manifest.json

themes/hugo-book/assets/menu-reset.js

themes/hugo-book/assets/mermaid.json