docs(readme): incorrect pnpm script

[Jay-Karia]

Related page

https://github.com/mui/material-ui/blob/next/CONTRIBUTING.md

Kind of issue

Other

Issue description

Here: https://github.com/mui/material-ui/blob/next/CONTRIBUTING.md#trying-changes-on-the-documentation-site
there is a pnpm script mentioned to start the development server: pnpm start which is incorrect. It should be rather pnpm dev.

We use pnpm start after building the application.

Context

This is mentioned in CONTRIBUTING.md file.
We have to use pnpm dev to start the local development server.

Search keywords: pnpm, docs, readme

[Janpot]

The start script runs pnpm install && pnpm docs:dev. While it's a bit unusual to call this script start, it doesn't seem wrong to me. I'm not sure who is using this script, but I wouldn't want to mess with their muscle memory considering it's been there for at least six years as far as i can see.