added and linked SECURITY.md

[daniel-jettka]

Description, Context and related Issue

added SECURITY.md and linked in README

Refs #430

How Has This Been Tested?

Had a look how the MDs look like in branch

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation Update

Checklist

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have performed a self-review of my code
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[krHERO]

looks totally fine, thanks!