Docs: Consistent use of npm in terminal command examples

[Mosaab-Emam]

What is the documentation issue?

On the installation page there is a single use of pnpm in a terminal command example. This is inconsistent with the use of npm on the rest of the examples on this page.

Is there any context that might help us understand?

Consistency is good.
It's always possible in the future to render multiple versions of a command (e.g., npm, pnpm, bun) to appeal to developer preferences.

Does the docs page already exist? Please link to it.

https://nextjs.org/docs/app/getting-started/installation#run-the-development-server