Document how to preserve custom .npmrc content when using PNPM #4458
Description
When using PNPM, Vaadin creates a custom .npmrc file in the project root folder.
If it detectes an existing file, it overwrites it if the NOTICE: this is an auto-generated file comment is found.
The .npmrc file is not generated if the project is configured to use NPM.
Documentation should have a note about removing the comment when a customized .nomrc file is required.
See https://vaadin.com/forum/t/using-pnpm-generates-a-dot-npmrc-that-you-cannot-alter/178365