Add portaudio19-dev system dependency to installation instructions

Author: claude

README.md

@@ -32,7 +32,13 @@ A minimalist real-time synthesizer built in Python using the keyboard as a piano
 
 ## Installation
 
-Install dependencies using `uv`:
+First, install the required system package:
+
+```bash
+sudo apt install portaudio19-dev
+```
+
+Then install Python dependencies using `uv`:
 
 ```bash
 uv sync