Add profiling instructions

Author: Yatekii

README.md

@@ -25,3 +25,13 @@ cargo run --release -- -t 14/8580/5737
 ```
 
 Use any number of `-t` args to load multiple tiles. If no args are passed, load a full map.
+
+# Profiling heap on macOS with Instruments
+
+Install `cargo-instruments`
+
+```
+brew install cargo-instruments
+```
+
+Run `cargo instruments -t Allocations --release --time-limit 30000` and look at the generated trace in `target/instruments`.