[node.js] How can I add a .npmrc file?

I installed node on my Mac OS Sierra. I use Windows at my work so there I have a .npmrc file in the node folder but I don't seem to find that in mac. The problem is I want to add a registry of the format

    "scope=rohit-project@rohit-aquila:registry=https://registry.npmjs.org/
    //registry.npmjs.org/:_authToken=03408522-4rfca-dff4f-dfsf-43863gfe3492"

How do I add it so that I can install the dependencies and modules for my project by running npm install on MAC OS Sierra.

I created a .npmrc file simply and added the above code...and therefater running npm install I get the following error

    rohitsrivastava$ npm install
    npm ERR! Darwin 16.4.0
    npm ERR! argv "/usr/local/bin/node" "/usr/local/bin/npm" "install"
    npm ERR! node v7.7.3
    npm ERR! npm  v4.1.2
    npm ERR! code E404

    npm ERR! 404 Not found : @rohit-project/notes
    npm ERR! 404 
    npm ERR! 404  '@rohit-project/notes' is not in the npm registry.
    npm ERR! 404 You should bug the author to publish it (or use the name yourself!)
    npm ERR! 404 It was specified as a dependency of '@rohit-project/mega'
    npm ERR! 404 
    npm ERR! 404 Note that you can also install from a
    npm ERR! 404 tarball, folder, http url, or git url.

In MacOS Catalina 10.15.5 the .npmrc file path can be found at

/Users/<user-name>/.npmrc

Open in it in (for first time users, create a new file) any editor and copy-paste your token. Save it.

You are ready to go.

Note: As mentioned by @oligofren, the command npm config ls -l will npm configurations. You will get the .npmrc file from config parameter userconfig

Assuming you are using VSTS run vsts-npm-auth -config .npmrc to generate new .npmrc file with the auth token

This issue is because of you having some local or private packages. For accessing those packages you have to create .npmrc file for this issue. Just refer the following link for your solution. https://nodesource.com/blog/configuring-your-npmrc-for-an-optimal-node-js-environment