message: docs: update duplicate note on package use
diff: <img src="https://raw.githubusercontent.com/pact-foundation/pact-logo/master/media/logo-black.png" width="200">
  +| :information_source: |
  +|-----------------------------------------|
  +| This is a core library, designed for use in the bowels of another package. Unless you are wanting to develop tools for the pact ecosystem, you almost certainly want to install [`@pact-foundation/pact`](https://github.com/pact-foundation/pact-js/) instead|
  +
  ![Build and test](https://github.com/pact-foundation/pact-js-core/workflows/Build%20and%20test/badge.svg)
  [![Known Vulnerabilities](https://snyk.io/test/github/pact-foundation/pact-js-core/badge.svg?targetFile=package.json)](https://snyk.io/test/github/pact-foundation/pact-js-core?targetFile=package.json)
  [![npm](https://img.shields.io/npm/v/@pact-foundation/pact-core.svg)](https://www.npmjs.com/package/@pact-foundation/pact-core)
  # Pact-JS Core
  -**This is the core of pact-js. Unless you are wanting to develop tools for the pact ecosystem, you almost certainly want to install [`@pact-foundation/pact`](https://github.com/pact-foundation/pact-js/) instead**.
  -
  A wrapper for the [Pact](http://pact.io) [CLI Tools](https://github.com/pact-foundation/pact-ruby-standalone).
  -***If you are new to Pact and are wanting to get started with contract testing, you almost certainly don't want to use this package. Head over to [Pact JS](https://github.com/pact-foundation/pact-js/) instead.**
  -
  <!-- TOC -->
  - [Pact-JS Core](#pact-js-core)
  