docs(README.md) update details

- Fix details about minimum Node.js versions required.
- Fix capitalization of tool names (SASS --> Sass).
- Improve structure of English language sentences.
- Run `gulp dev:doc` to update Table of Contents.
- Improve Markdown syntax to fix markdownlint warnings:
  - MD022/blanks-around-headers: Headers should be surrounded by blank lines
  - MD009/no-trailing-spaces: Trailing spaces [Expected: 0; Actual: 2]
  - MD031/blanks-around-fences: Fenced code blocks should be surrounded by blank lines
  - MD032/blanks-around-lists: Lists should be surrounded by blank lines
  - MD004/ul-style: Unordered list style [Expected: dash; Actual: asterisk]
  - MD040/fenced-code-language: Fenced code blocks should have a language specified
  - MD034/no-bare-urls: Bare URL used
  - MD012/no-multiple-blanks: Multiple consecutive blank lines [Expected: 1; Actual: 2]