Create SECURITY-NOTICE.md

[mmogy]

** READ THIS FIRST! **

Are you implementing a new feature?

Requests for new features should first be discussed on the discussion forum.
This allows the community to gather feedback and assess whether or not there is
an existing way to achieve the desired functionality.

If it is determined that a new feature needs to be implemented, include a link
to the relevant discussion along with the pull request.

Is this a security patch?

Do not open pull requests that might have security implications. Potential
security vulnerabilities should be reported privately to jaredhanson@gmail.com.
Once any vulerabilities have been repaired, the details will be disclosed
publicly in a responsible manner. This also allows time for coordinating with
affected parties in order to mitigate negative consequences.

Checklist

• I have read the CONTRIBUTING guidelines.
• I have added test cases which verify the correct operation of this feature or patch.
• I have added documentation pertaining to this feature or patch.
• The automated test suite ($ make test) executes successfully.
• The automated code linting ($ make lint) executes successfully.

[coveralls]

Coverage remained the same at 77.193% when pulling 95e69ee on mmogy:add-security-notice into 0c08f97 on jaredhanson:master.

[radekk]

LGTM 👍