README.md needs fixing now that corepack is not bundled with nodejs

[jackmtpt]

The current text says: We do acknowledge the irony and overhead of using npm to install Corepack, which is at least part of why the preferred option is to use the Corepack version that is distributed along with Node.js itself.

However as of node 25 there is no version of corepack distributed with nodejs, so the preferred option is now not possible to use.

[aduh95]

It is possible to use if you use e.g. Node.js 24, which is supported until 2028-04-30, and that's still the preferred option atm

[jackmtpt]

Sure, that's likely what we're going to do, but the readme still needs updating for anyone using node >= 25