message: docs: Add information to README about Docker image & Docker Hub
  closes
diff: [![Build Status](https://travis-ci.org/Rebilly/ReDoc.svg?branch=master)](https://travis-ci.org/Rebilly/ReDoc) [![Coverage Status](https://coveralls.io/repos/Rebilly/ReDoc/badge.svg?branch=master&service=github)](https://coveralls.io/github/Rebilly/ReDoc?branch=master) [![dependencies Status](https://david-dm.org/Rebilly/ReDoc/status.svg)](https://david-dm.org/Rebilly/ReDoc) [![devDependencies Status](https://david-dm.org/Rebilly/ReDoc/dev-status.svg)](https://david-dm.org/Rebilly/ReDoc#info=devDependencies) [![npm](http://img.shields.io/npm/v/redoc.svg)](https://www.npmjs.com/package/redoc) [![License](https://img.shields.io/npm/l/redoc.svg)](https://github.com/Rebilly/ReDoc/blob/master/LICENSE)
  - [![bundle size](http://img.badgesize.io/https://cdn.jsdelivr.net/npm/redoc/bundles/redoc.standalone.js?compression=gzip&max=300000)](https://cdn.jsdelivr.net/npm/redoc/bundles/redoc.standalone.js) [![npm](https://img.shields.io/npm/dm/redoc.svg)](https://www.npmjs.com/package/redoc) [![](https://data.jsdelivr.com/v1/package/npm/redoc/badge)](https://www.jsdelivr.com/package/npm/redoc)
  + [![bundle size](http://img.badgesize.io/https://cdn.jsdelivr.net/npm/redoc/bundles/redoc.standalone.js?compression=gzip&max=300000)](https://cdn.jsdelivr.net/npm/redoc/bundles/redoc.standalone.js) [![npm](https://img.shields.io/npm/dm/redoc.svg)](https://www.npmjs.com/package/redoc) [![](https://data.jsdelivr.com/v1/package/npm/redoc/badge)](https://www.jsdelivr.com/package/npm/redoc) [![Docker Build Status](https://img.shields.io/docker/build/redocly/redoc.svg)](https://hub.docker.com/r/redocly/redoc/)
  </div>
  @@ -184,6 +184,17 @@ You can also specify `onLoaded` callback which will be called each time Redoc ha
  />
  ```
  +## The Docker way
  +
  +ReDoc is available as pre-built Docker image in official [Docker Hub repository](https://hub.docker.com/r/redocly/redoc/). You may simply pull & run it:
  +
  + docker pull redocly/redoc
  + docker run -p 80:8080 redocly/redoc
  +
  +Also you may rewrite some predefined environment variables defined in [Dockerfile](./Dockerfile). By default ReDoc starts with demo Petstore spec located at `http://petstore.swagger.io/v2/swagger.json`, but you may change this URL using environment variable `SPEC_URL`:
  +
  + docker run -p 80:8080 -e SPEC_URL=https://api.example.com/openapi.json redocly/redoc
  +
  ## ReDoc CLI
  [See here](https://github.com/Rebilly/ReDoc/blob/master/cli/README.md)
  