Update readme

README.md

@@ -11,3 +11,23 @@ cargo run
 ```
 
 To exit the simulation, press q, ESC or Ctrl+c.
+
+## Tests
+
+A few tests can be run with:
+
+```sh
+cargo test
+```
+
+## Benchmarks
+
+`cargo bench` runs benchmarks. Their results are available under `target/criterion/report/index.html`.
+
+## Simulation
+
+* The world is a simple two-dimensional rectangle with integer positions
+* Agents can occupy the same space
+* Agents can make one move per simulation step, either by trying to move by at most one unit in both directions or by trying to tag another actor
+* Agents need to be at most one unit away in both directions from others in order to tag them
+* Agents act at the same time and their actions are validated against the previous state