Add dependabot (#84)

Author: johnwason

.github/dependabot.yml

@@ -0,0 +1,15 @@
+version: 2
+
+updates:
+  # Keep GitHub Actions workflows up to date
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+      day: "monday"
+      time: "06:00"
+      timezone: "America/Chicago"
+    labels:
+      - "dependencies"
+      - "github-actions"
+    open-pull-requests-limit: 5