refactor: organize src modules by category

README.md

@@ -4,12 +4,20 @@ Test repository for pipe system simulation work.
 
 ## Structure
 
+- `src/tank_pipe/` 0D-1D tank-pipe blowdown simulation
+- `src/cylinder/` high-pressure gas cylinder model
+- `src/cryo_tank/` cryogenic LN2 tank simulation
+- `src/main.py` compatibility entry point for the tank-pipe simulation
 - `docs/` design notes and reports
-- `src/` source code
 - `cases/` test cases and input data
 - `scripts/` utility scripts
 - `results/` generated outputs and post-processing summaries
 
-## Status
+## Common Commands
 
-Initial repository scaffold created.
+```bash
+python3 src/main.py
+python3 src/tank_pipe/main.py
+python3 src/cryo_tank/main.py
+pytest -q
+```