Adjusted security policy (#1107)

Author: sliverc

SECURITY.md

@@ -4,6 +4,6 @@
 
 If you believe you've found something in Django REST framework JSON:API which has security implications, please **do not raise the issue in a public forum**.
 
-Send a description of the issue via email to [rest-framework-jsonapi-security@googlegroups.com][security-mail]. The project maintainers will then work with you to resolve any issues where required, prior to any public disclosure.
+Use the security advisory to [report a vulnerability](https://github.com/django-json-api/django-rest-framework-json-api/security/advisories/new) instead.
 
-[security-mail]: mailto:[email protected]
+The project maintainers will then work with you to resolve any issues where required, prior to any public disclosure.

docs/CONTRIBUTING.md

@@ -69,4 +69,3 @@ In case a new maintainer joins our team we need to consider to what of following
 * [Github organization](https://github.com/django-json-api)
 * [Read the Docs project](https://django-rest-framework-json-api.readthedocs.io/)
 * [PyPi project](https://pypi.org/project/djangorestframework-jsonapi/)
-* [Google Groups security mailing list](https://groups.google.com/g/rest-framework-jsonapi-security)