Trivial issue in readme.md

[johnkelaita]

Prerequisites

• I am running the latest version
• I checked the documentation and found no answer
• I checked to make sure that this issue has not already been filed
• I'm reporting the issue to the correct repository (for multi-repository projects)

Expected Behavior

On a freshly installed system, I can install yarn according to the documentation.

Current Guideline

yarn install -g yarn

Failure Information (for bugs)

Yarn must be installed in order to globally install yarn.

Steps to Reproduce

Run the above command on a system without yarn.

1. yarn install -g yarn
2. yarn: command not found

Context

• NPM installed: Yes
• Firmware Version: Any
• Operating System: Any
• SDK version: Any
• Toolchain version: Any

Failure Logs

Command line error - could affect pipeline builds.

Suggested resolve

1. Amend the docs to require npm to be installed first
2. Suggest the installation of yarn via npm (ie. npm i -g yarn)