docs(readme): fix broken image paths, wrong section reference, and minor typos

- README.md / README-EN.md: the MindSpider example image used a
  backslash path (`MindSpider\img\example.png`), which GitHub does not
  render. Switch to a forward slash so the image displays.
- README-EN.md: section 6.1 Note 2 referenced "section 5.3" but the
  crawler section is 6.3.
- README-EN.md: missing space after the colon before a Markdown link
  (`instructions:[Configure...]` -> `instructions: [Configure...]`).
- README.md / README-EN.md: the `.env` example was tagged as `yml` but
  the content is shell-style `KEY=VALUE` — switch the code-block
  language tag to `bash` for accurate syntax highlighting.
- README.md: pronoun typo「把他变成」->「把它变成」(it refers to the
  system, which takes 它 in modern standard Chinese).
- README.md: product-name casing `openAI` -> `OpenAI`.