add renovate.json (#2)

Author: jgallagher

.github/renovate.json

@@ -0,0 +1,8 @@
+{
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "extends": [
+    "local>oxidecomputer/renovate-config",
+    "local>oxidecomputer/renovate-config//rust/autocreate",
+    "local>oxidecomputer/renovate-config//actions/pin"
+  ]
+}