Update Docker_Security_Cheat_Sheet.md

[gbrindisi]

Adding a reference for Dockerfile best practices.

This PR covers issue #504

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[mackowski]

Hey thanks for this PR. In addition to the link please find the practices that are missing or should be updated in the cheatsheet and add them to it to make the recommendations better.

[gbrindisi]

@mackowski hey there! I've added a new rule to address Dockerfile linting

[mackowski]

Awesome, thank you!