message: docs: improve readme
  [ci skip]
diff: ## Features
  - Extremely easy deployment
  +- [redoc-cli](https://github.com/Rebilly/ReDoc/blob/master/cli/README.md) with ability to bundle your docs into **zero-dependency** HTML file
  +- Server Side Rendering ready
  - The widest OpenAPI v2.0 features support (yes, it supports even `discriminator`) <br>
  ![](docs/images/discriminator-demo.gif)
  +- OpenAPI 3.0 support
  - Neat **interactive** documentation for nested objects <br>
  ![](docs/images/nested-demo.gif)
  - Code samples support (via vendor extension) <br>
  ![](docs/images/code-samples-demo.gif)
  -- Progressive loading with `lazy-rendering` options <br>
  -![](docs/images/progressive-loading-demo.gif)
  - Responsive three-panel design with menu/scrolling synchronization
  - Integrate API Introduction into side menu - ReDoc takes advantage of markdown headings from OpenAPI description field. It pulls them into side menu and also supports deep linking.
  - High-level grouping in side-menu via [`x-tagGroups`](docs/redoc-vendor-extensions.md#x-tagGroups) vendor extension
  -- Multiple ReDoc instances on single page ([example](demo/examples/multiple-apis/index.html))
  +- Simple integration with `create-react-app` ([sample](https://github.com/APIs-guru/create-react-app-redoc))
  +- Branding/cusomizations via [`theme` option](#redoc-options-object)
  ## Roadmap
  - [x] ~~[OpenAPI v3.0 support](https://github.com/Rebilly/ReDoc/issues/312)~~
  