[DOCS] Outdated "Building a node from source"

[Hugoo]

Description

This [building a node from source page] is totally outdated. It has some pnpm install related instructions which are from more than 2 years ago.

The optimism monorepo https://github.com/ethereum-optimism/optimism has no package.json or js related files to perform such actions.

The correct instructions can be found here:

https://github.com/ethereum-optimism/optimism/tree/develop/op-node#usage

Acceptance criteria

Anyone following this tutorial should be able to build from source.

[sbvegan]

Thank you for creating this issue, I've fixed these docs in this PR: #1461

[Hugoo]

Great thanks 😊👍