message: docs: add github action to generate doc
  Added github action install dependencies required to generate
  documentation and then run the documentation generator.
  As a final step publish the changes to `gh-pages` branch which will be
  the source for github documentation.
  Adds badge for doc-generator github action
  closes:
diff: -# ts-jest [![npm version](https://badge.fury.io/js/ts-jest.svg)](https://badge.fury.io/js/ts-jest) [![NPM downloads](https://img.shields.io/npm/dm/ts-jest.svg?style=flat)](https://npmjs.org/package/ts-jest) [![Known Vulnerabilities](https://snyk.io/test/github/kulshekhar/ts-jest/badge.svg)](https://snyk.io/test/github/kulshekhar/ts-jest) [![Coverage Status](https://coveralls.io/repos/github/kulshekhar/ts-jest/badge.svg?branch=master)](https://coveralls.io/github/kulshekhar/ts-jest?branch=master) [![Dependabot Status](https://api.dependabot.com/badges/status?host=github&repo=kulshekhar/ts-jest)](https://dependabot.com) [![Build Status](https://travis-ci.com/kulshekhar/ts-jest.svg?branch=master)](https://travis-ci.com/kulshekhar/ts-jest)
  +# ts-jest
  +
  +[![npm version](https://badge.fury.io/js/ts-jest.svg)](https://badge.fury.io/js/ts-jest)
  +[![NPM downloads](https://img.shields.io/npm/dm/ts-jest.svg?style=flat)](https://npmjs.org/package/ts-jest)
  +[![Known Vulnerabilities](https://snyk.io/test/github/kulshekhar/ts-jest/badge.svg)](https://snyk.io/test/github/kulshekhar/ts-jest)
  +[![Coverage Status](https://coveralls.io/repos/github/kulshekhar/ts-jest/badge.svg?branch=master)](https://coveralls.io/github/kulshekhar/ts-jest?branch=master)
  +[![Dependabot Status](https://api.dependabot.com/badges/status?host=github&repo=kulshekhar/ts-jest)](https://dependabot.com)
  +[![Build Status](https://travis-ci.com/kulshekhar/ts-jest.svg?branch=master)](https://travis-ci.com/kulshekhar/ts-jest)
  +[![doc-generator](https://github.com/kulshekhar/ts-jest/workflows/doc-generator/badge.svg)](https://github.com/kulshekhar/ts-jest/actions)
  <img src="./icon.png" align="right" title="ts-jest Logo" width="128" height="128">
  