Delete CONTRIBUTING.md (#1)
Delete CONTRIBUTING.md (#1)

Delegate to `.github` organization repo.

Depends on https://github.com/google-github-actions/.github/pull/10.

Signed-off-by: Seth Vargo <25a3b6cc85a8cde49f8b0f9aa21c050bc04072d4@sethvargo.com>
google-github-actions/github-runner-token-proxy