Add security policy

Author: benz0li

SECURITY.md

@@ -0,0 +1,19 @@
+## Supported Versions
+
+Only the docker image with the latest version of Python is supported with
+security updates.
+
+## Reporting a Vulnerability
+
+To report a vulnerability in the latest docker image, email the maintainer
+olivier.benz@b-data.ch.
+
+## Vulnerabilities in Prior Versions
+
+Vulnerabilities in docker images with prior versions of Python are not fixed.
+
+Whenever a new version of Python is released, the previous version's docker
+image is rebuilt once again and then frozen.
+
+Docker images *may* be rebuilt or extended if they fail to start or have runtime
+issues.