Document DEBUG environment variable

[MikeMcC399]

Current state

• The corepack repo is configured to use the npm module debug and there have been enhancements such as chore: include install directory in debug log #111 and fix: make DEBUG=corepack more useful #538 to improve the usefulness of the debug output.

• Neither the README document, nor the CONTRIBUTING document mention debug. There is no information about how to set the environment variable DEBUG or what additional output can be expected if it is set.

Suggestion

1. Add DEBUG=corepack to the README document.
2. Note in the CONTRIBUTING document that DEBUG=corepack should not be set when running yarn test as the additional output may cause the tests to fail.

[MikeMcC399]

• PR docs: add DEBUG=corepack logging instructions #605 submitted to resolve this request