Yeoman Generator

This is a command-line scaffolding tool that lets you quickly assemble a web project that has all the required components and dependencies.
The Yeoman Generator is an open source client side scaffolding tool for creating web applications:
link - yeoman.io/generators/
link - github.com/officedev/generator-office
link - npmjs.com/package/generator-office

Install Yeoman

open the command prompt
Install the Yeoman generator globally

npm install -g yo 

installs to the following location:

C:\users\russell\AppData\Roaming\npm\node_modules\yo 

To check your version of Yeoman Generator is installed

yo --version                       // 4.3.0 

This will display the version number and also tell you what the latest version is.
To install the latest update

npm install -g yo 

Install the 'generator-office' Generator

link - npmjs.com/package/generator-office

npm install -g generator-office 

installs to the following location:

C:\users\russell\AppData\Roaming\npm\node_modules\generator-office 

Browse to a new local folder

cd C:\temp\yeoman-sample\ 
yo Office 

The welcome screen will be displayed.
It will prompt you for the following information:
SS
choose a project type: Add-in using React
name: ExcelYoSample
client application: Excel
This will create all the files and folders that are required
(C:\temp\yeoman-sample\)

type "code ." code space full stop, to launch VS Code

C:\code\office\yeoman > nodist 4.4.4 
C:\code\office\yeoman > git --version 
C:\code\office\yeoman > npm -v 
C:\code\office\yeoman > npm install -g bower 
C:\code\office\yeoman > npm install -g gulp 
C:\code\office\yeoman > npm install -g tsd 

C:\code\office\yeoman > gulp serve 

Create a manifest file for existing project

Move to the parent folder

cd parent-folder 
create-react-app my-addin1 

Generate a manifest file for your add-in using the Yeoman generator

cd my-addin1 
yo office 

new subfolder - no
name of your addin - MyAddin1
which application - Excel
create new addin - no
open resource.html - no
overwrite package.json - no
sideload the add-in into Excel
use a shared folder catalog to sideload your new addin with Excel