chore: add security policy

SECURITY.md

@@ -0,0 +1,21 @@
+# Security Policy
+
+The `rules_graalvm` package has a very small surface area of possible vulnerability; while it does perform downloads (within the scope of Bazel's protections and tools), all downloaded material
+is hashed, fingerprinted, and checked.
+
+Downloaded components by GraalVM's `gu` tool cannot be checked, but GraalVM provides their own security assurances for these packages. The `rules_graalvm` package is only meant to be used at build-time
+in a developer's Bazel workspace.
+
+## Supported Versions
+
+All versions of this package are supported as of the `v0.9.0` release.
+
+| Version | Supported |
+| ------- | ------------------ |
+| 0.9.0+ | :white_check_mark: Yep |
+| `rules_graal` | :x: Deprecated |
+
+## Reporting a Vulnerability
+
+To report a vulnerability, use the [GitHub Issues](https://github.com/sgammon/rules_graalvm/issues) tracker. If you need to report a vulnerability privately, please send an email to the author. You can
+@sgammon's contact information in commits and elsewhere.