docs: update README

[Ir1d]

• add en version (brief)
• add screenshot to README
• update list of features （如下）
• package.json （见下方链接）

参考：

• https://www.gatsbyjs.org/contributing/submit-to-starter-library/
• https://www.gatsbyjs.org/contributing/site-showcase-submissions/
• https://docs.npmjs.com/creating-a-package-json-file

待填写：

- url: https://ng.oi-wiki.org/
  repo: https://github.com/OI-wiki/gatsby-oi-wiki
  description: Generate material style modern docs/tutorial/wiki websites using Gatsby + MDX
  tags:
  - Documentation
  - Markdown
  - Official
  - MDX
  - Search
  - SEO
  - PWA
  - Language:TypeScript
  - Linting
  - Netlify
  - Styling:CSS-in-JS
  features:
    - Write using Markdown / MDX
	- Material style theme
	- Syntax Highlighting using VS Code's engine
	- Search Integration with Elasticsearch
	- Progressive Web App, Works Offline
	- [ ] Google Analytics Integration
	- Automatically generated sidebar navigation, table of contents, previous/next
	- Dark Mode toggle
	- Edit on Github
	- Fully customisable
	- [ ] Rich embeds and live code editor using MDX
	- [ ] Easy deployment: Deploy on Netlify / Now.sh / Docker

[cbw2007]

package.json也需要改（

[cbw2007]

"private": true,
"name": "demo",
"version": "0.0.0",
"license": "MIT",

[cbw2007]

package.json也需要改（

https://docs.npmjs.com/creating-a-package-json-file 补充

[cbw2007]

有待商榷

[cbw2007]

待填写：

• author - 包的作者姓名。
• contributors - 包的其他贡献者姓名。