add configuration for codesandbox-ci (#235)

Author: phryneas

.codesandbox/ci.json

@@ -0,0 +1,10 @@
+{
+  // a list of sandboxes that you want generated for a PR, if this list
+  // is not set we will default to `vanilla`. The built library will automatically
+  // be installed in the fork of these sandboxes.
+  "sandboxes": [
+    "vanilla",
+    "vanilla-ts",
+    "github/reduxjs/rsk-github-issues-example"
+  ]
+}