Copy over Wire tutorial from Go Cloud (#86)

Originally authored by @enocom. Added to CONTRIBUTORS.

Fixes #80

_tutorial/wire_gen.go

@@ -0,0 +1,18 @@
+// Code generated by Wire. DO NOT EDIT.
+
+//go:generate wire
+//+build !wireinject
+
+package main
+
+// Injectors from wire.go:
+
+func InitializeEvent(phrase string) (Event, error) {
+	message := NewMessage(phrase)
+	greeter := NewGreeter(message)
+	event, err := NewEvent(greeter)
+	if err != nil {
+		return Event{}, err
+	}
+	return event, nil
+}