Add a SECURITY.md

[mcafaro]

All our repos need to have a SECURITY.md file in the root containing the following content:

# Reporting Security Vulnerabilities 

If you believe you have discovered a security vulnerability, please report it to 
[security@mathworks.com](mailto:security@mathworks.com). Please see 
[MathWorks Vulnerability Disclosure Policy for Security Researchers](https://www.mathworks.com/company/aboutus/policies_statements/vulnerability-disclosure-policy.html) 
for additional information.

[nbhoski]

Merged the code #163