scenario2: add perf

scenario1-python-to-c/README.md

@@ -38,6 +38,8 @@ py-spy record -o prime_slow.svg -- python3 prime_slow.py
 
 Open `prime_slow.svg` in a browser. The widest bar at the top shows where time is spent.
 
+**Note:** py-spy only traces Python functions. Time spent in native C code (like the C library calls in later steps) won't appear in py-spy flamegraphs.
+
 ### Step 4: Compile and run the partially optimized version
 ```bash
 # Compile the C library