Only allow pnpm

When you use pnpm on a project, you don't want others to accidentally run npm install or yarn. To prevent devs from using other package managers, you can add the following preinstall script to your package.json:

{    "scripts": {        "preinstall": "npx only-allow pnpm"    }}

Now, whenever someone runs npm install or yarn, they'll get an error instead and installation will not proceed.

If you use npm v7, use npx -y instead.