fix README formatting

detailed list of changes:

fix code formatting of `index.less` – GitHub-Flavored Markdown is not supported in repository files

add inline code formatting

change the “Version”: “1.0” section to a prettier and more-semantic `<dl>` definition list

since all headings have the wrong number of underlines, just change to three underlines, so they don’t need to be maintained in the future

fix grammar, capitalization, and typography

make “LESS” a link in case someone stumbles on this project without knowing what it is

add blank lines between sections to make them more visually distinguishable