Revise security policy for supported versions

Updated the supported versions and reporting instructions.

Author: wellington36

SECURITY.md

@@ -0,0 +1,13 @@
+# Security Policy
+
+## Supported Versions
+
+| Version | Supported          |
+| ------- | ------------------ |
+| 1.1.x   | :white_check_mark: |
+| 1.0.5   | :white_check_mark: |
+| < 1.0.5 | :x:                |
+
+## Reporting a Vulnerability
+
+If you'd like to contribute, consider opening an issue here: [https://github.com/wellington36/InfSumPy/issues](https://github.com/wellington36/InfSumPy/issues).