CI: Add dynamic SECURITY.md

Adds CI workflow to dynamically update `SECURITY.md` anytime its
[source][] changes.

[source]: https://github.com/thoughtbot/templates/blob/main/SECURITY.md.template

Author: stevepolitodesign

.github/workflows/dynamic-security.yml

@@ -0,0 +1,19 @@
+name: update-security
+
+on:
+  push:
+    paths:
+      - SECURITY.md
+    branches:
+      - main
+  workflow_dispatch:
+
+jobs:
+  update-security:
+    permissions:
+      contents: write
+      pull-requests: write
+      pages: write
+    uses: thoughtbot/templates/.github/workflows/dynamic-security.yaml@main
+    secrets:
+      token: ${{ secrets.GITHUB_TOKEN }}

SECURITY.md

@@ -0,0 +1,2 @@
+<!-- START /templates/security.md -->
+<!-- END /templates/security.md -->