compare-report: median-of-reps grouping, --exclude, --results

--group NAME=t1,t2 collapses repetitions into one median column per device,
--exclude drops bad runs, and --results reads a collected results directory.

README.md

@@ -383,6 +383,17 @@ are back-filled from the raw results (`fio` JSON, `openssl`, `7z`,
 `sysbench-mem`, `glmark2`/`vkmark`), so existing runs compare without re-running.
 Needs `matplotlib`; use `--no-graphs` for the table alone.
 
+With **median-of-3**, collapse repetitions into one column per device and drop
+any bad run:
+```bash
+python3 compare-report.py --results ~/Documents/results \
+  --group "desktop=before1-headless,before2-headless,before3-headless" \
+  --group "server=server1-headless,server2-headless,server3-headless" \
+  --group "t14=t14-2,t14-3"          # t14-1 dropped (low-battery run)
+```
+`--group NAME=t1,t2,...` makes one median column; `--exclude t1 t2` drops tags.
+`--results DIR` reads another machine's collected `results/`.
+
 Fill the results table in `benchmarks.txt` with the medians after each side.
 
 ---