docs: add quick demo and core architecture overview

Adds a quick demo command using `cargo run -p example-tui` to launch a minimalist TUI with demo scores.

Also includes a core architecture diagram and overview in the README for better understanding of the project structure.

README.md

@@ -1,9 +1,13 @@
-### Watch the whole repo on every change
+# Harmony : Open Infrastructure Orchestration
 
-Due to the current setup being a mix of separate repositories with gitignore and rust workspace, a few options are required for cargo-watch to have the desired behavior :
+## Quick demo
 
-```sh
-RUST_LOG=info cargo watch --ignore-nothing -w harmony -w private_repos/ -x 'run --bin nationtech' 
-```
+`cargo run -p example-tui`
 
-This will run the nationtech bin (likely `private_repos/nationtech/src/main.rs`) on any change in the harmony or private_repos folders.
+This will launch Harmony's minimalist terminal ui which embeds a few demo scores.
+
+Usage instructions will be displayed at the bottom of the TUI.
+
+## Core architecture
+
+![Harmony Core Architecture](docs/diagrams/Harmony_Core_Architecture.drawio.svg)