Update documentation to include usage of TruffleHog rules

GitLab uses a ruleset from TruffleHog and Gitleaks. This is commented here https://gitlab.com/gitlab-org/security-products/analyzers/secrets/-/blob/master/gitleaks.toml#L64

# rules from trufflehog

I'd like to pull request the documentation to credit TruffleHog as well since currently GitLeaks is all that's mentioned.