docs: add DEBUG=corepack logging instructions

[MikeMcC399]

• closes Document DEBUG environment variable #603

Change

Add information to the following documents regarding use of the npm debug module by setting the related environment variable DEBUG=corepack to enable additional debug logging:

• README document and
• CONTRIBUTING document Edit: removed this change

[MikeMcC399]

Preview

• https://github.com/MikeMcC399/corepack/blob/docs/debug/README.md#troubleshooting
• https://github.com/MikeMcC399/corepack/blob/docs/debug/CONTRIBUTING.md#contributing-to-corepack

[MikeMcC399]

@aduh95

Thank you for merging the documentation change! 👍🏻

When the CI test ran on the merge it has failed on random configurations with:

❯ tests/config.test.ts (1 test | 1 failed) 158ms
× key store should be up-to-date > should contain up-to-date npm keys

See https://github.com/nodejs/corepack/actions/runs/12969630436

It looks like npm is in the process of updating their keys and that some servers have been updated, and others have not. This should probably be tracked in a separate issue if it doesn't resolve itself on its own.

• See config.test randomly failing in CI (key store should be up-to-date) #611