added welcome message file

spaces/welcome_message.md

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+## Welcome!
+
+*⚠️ This is a private demo using my own OpenAI API key. Please use responsibly. ⚠️*
+
+This chatbot uses retrieval augmented generation (RAG) to answer questions about topics
+that are discussed in my master thesis. My master thesis can be found on the [GitHub repo](https://github.com/leonardpasi/mythesis-chatbot) of the project.
+
+Here you get to choose between three RAG techniques:
+- **classic retrieval** (which includes a reranker model, so it's actually not the simplest RAG imaginable)
+- **sentence window retrieval**
+- **auto-merging retrieval**
+
+Feel free to experiment with different modes! Note that a little extra delay is to be expected when switching to another mode.
+Also, note that all your queries (as well as system responses) are automatically logged on a remote PostgreSQL database for continuous monitoring of the deployed systems.
+
+Each of these systems has been optimized for performance by doing a grid search on the
+relevant parameters. Performance is quantified with five metrics:
+- **context relevance**: is the retrieved context relevant to the query?
+- **groundedness**: is the response supported by the context?
+- **answer relevance**: is the response relevant to the query?
+- **cost**
+- **latency**