Clarify behaviour of exclude_regexes_capture and exclude_regexes_match

[jay4ay]

Updating description to clarify what these options do based on the logic at https://github.com/trufflesecurity/trufflehog/blob/8d144c2ba305fdcf2765b85c7ac08b6a7705a61b/pkg/custom_detectors/custom_detectors.go#L141 and based on my testing.

Description:

Explain the purpose of the PR.

Checklist:

• [ ] Tests passing (make test-community)?
• [ ] Lint passing (make lint this requires golangci-lint)?

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[dustin-decker]

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