Update docs, add Editor script: Create Druid GUI Script, add simple using widgets example

druid/templates/druid.gui_script.template

@@ -0,0 +1,21 @@
+local druid = require("druid.druid")
+
+function init(self)
+    self.druid = druid.new(self)
+end
+
+function final(self)
+    self.druid:final()
+end
+
+function update(self, dt)
+    self.druid:update(dt)
+end
+
+function on_message(self, message_id, message, sender)
+    self.druid:on_message(message_id, message, sender)
+end
+
+function on_input(self, action_id, action)
+    return self.druid:on_input(action_id, action)
+end