Starter kits for DCO and credential scanning

[riverma]

Purpose

• To automatically ensure that contributors to a repo have "signed-off" on their developer certificate of origin (DCO) when pushing to a GitHub repo
• To automatically check if secrets/credentials (especially AWS ones) are not inadvertently committed to a repo (on the client side)

Proposed Changes

• [ADD] Starter kit for DCO "sign-offs"
• [ADD] Starter kit for secrets/credential scanning during Git commits

Issues

• [Improve Best Practice Guide]: Starter kits for patch integrity #26

Testing

• DCO scanner example: Update README.md riverma/terraformly#3
• git-secrets tested locally on machine successfully

[jpl-jengelke]

Looks great.