doc: Mention possibility of `corepack enable npm`
After reading https://www.totaltypescript.com/how-to-use-corepack, I realized that the Corepack docs page has some shortfalls:
- It implies npm is not supported, but npm is supported. It is just not enabled by default.
- The command for enabling the npm shim (
corepack enable npm
) is never mentioned anywhere.
With this PR, I believe to correct the docs according to the current implementation. If you anyways plan to change it, feel free to close.