docs: Update by_iter readme

runtime/experiments/applications/ekf/by_iteration/README.md

@@ -2,8 +2,10 @@
 
 Executes TinyEKF as shows by [You Chong's GPS example](http://www.mathworks.com/matlabcentral/fileexchange/31487-extended-kalman-filter-ekf--for-gps)
 
+This test executes multiple runs of three iterations (the output of a previous iteration is refed as input), comparing the binary result against a known memoized result stored in `initial_state.dat`, `one_iteration.dat`, `two_iterations.dat`, and `three_iterations.dat`.
+
+The `rust.sh` script stores per-run results to temporary files suffixed with `*.res.dat` and `diff -s` because I had trouble using cURL to pass a bash string of binary input.
+
 In order to be compatible with the stdin/stdout model of serverless, the input and output files are binary concatenations of various C structs.
 
 See `main()` in `runtime/tests/TinyEKF/extras/c/gps_ekf_fn.c` for specifics.
-
-This test executes multiple iterations, comparing the binary result against a known memoized result stored at `expected_result.dat`.