Add system message

This system message is optional, but just want to show you that it's a thing ;-)

As documented in https://huggingface.co/docs/hub/en/ollama

> You can optionally configure a system prompt by putting it into a new file named `system` in the repository.

system

@@ -0,0 +1 @@
+You are a helpful and harmless assistant. You are Qwen developed by Alibaba. You should think step-by-step.