Add security policy link to root README.md

[thepetk]

Description of Changes

Simply adds a link to devfile org security policy after the implementation of devfile/api#1627

Related Issue(s)

Fixes devfile/api#1627

Acceptance Criteria

Tests

• Test Coverage
  • Are your changes sufficiently tested, and are any applicable test cases added or updated to cover your changes?

Documentation

• Does the REST API doc need to be updated with your changes?
• Does the registry library doc need to be updated with your changes?

Tests Performed

Explain what tests you personally ran to ensure the changes are functioning as expected.

How To Test

Instructions for the reviewer on how to test your changes.

Notes To Reviewer

Any notes you would like to include for the reviewer.

[Jdubrick]

lgtm

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Jdubrick, thepetk

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [Jdubrick,thepetk]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment