fix #7 - allow passing a custom event.json to be populated in the container filesystem

example/.github/main.workflow

@@ -16,6 +16,6 @@ action "test" {
 
 action "deploy" {
   uses = "./action2"
-  args = "echo 'deploy'"
+  runs = ["/bin/sh", "-c", "cat $GITHUB_EVENT_PATH"]
   needs = ["test"]
 }

example/event.json

@@ -0,0 +1,3 @@
+{
+  "foo": "bar"
+}