Create SECURITY.md for 3.0.0 branch

[JoshHiles]

Description

Opening PR for merging in security policy into the 3.0.0 branch

Related Issue

#143

Motivation and Context

Currently no security policy in place so this allows better community involvement going forward

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

Checklist:

• I have read the CONTRIBUTING document.
• I have checked to ensure there aren't other open PULL REQUESTS for the same update/change.
• My code follows the code style of this project.
• I have updated the documentation accordingly where applicable.
• I have added tests to cover my changes.
• All new and existing tests passed.
• Coverage is 100% for new code.