README: bring back the serial stills example at SACLA as its own short walk-through

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HVeDQsU5a8AJUdJPgWevAK

README.md

@@ -145,14 +145,47 @@ deposited structure (`https://files.rcsb.org/download/4NWV.cif`).
 | [4NWV](https://www.rcsb.org/structure/4NWV) | SBGrid Data Bank [10.15785/sbgrid/9](https://doi.org/10.15785/sbgrid/9) | marCCD frames, 16.8 GB; a 400 A cell | 390 s |
 | [9V3D](https://www.rcsb.org/structure/9V3D) | CXIDB [236](https://cxidb.org/id-236.html), [10.11577/3014306](https://doi.org/10.11577/3014306) | MPCCD, Cheetah-SACLA HDF5; files `run157084-0..2.h5`, 10.1 GB | 35 s |
 
-Serial stills are given the known cell and space group and all the files of the run:
+### Serial stills: lysozyme at SACLA
+
+Serial data go through the same program. A dataset without a goniometer axis is taken as stills;
+give it the known cell and space group. The example is one run of a tape-drive experiment at SACLA
+BL2 (CXIDB 236): three of its hit files. The files carry the detector's panel layout, so no geometry
+file is needed.
 
 ```
+mkdir -p sacla236
+for f in run157084-0 run157084-1 run157084-2; do
+  curl -L -C - -o sacla236/$f.h5 https://cxidb.org/data/236/Data/lyso01-apo-bigXtal/$f.h5
+done
 curl -L -O https://files.rcsb.org/download/9V3D.pdb
 rugnux -o sacla236 -C 79.45,79.45,38.15,90,90,90 -S P43212 --model 9V3D.pdb sacla236/run157084-*.h5
 ```
 
-It indexes 95 % of the 2424 frames, merges to 1.7 A and refines the model to an R-free of 0.17.
+It takes about 35 s and ends with
+
+```
+ Result        WARNINGS: Merged to 1.69 A in P 43 21 2. 2 conditions need
+               attention: MODEL_FREE_SET, OVERLOADS.
+ Space group   P 43 21 2
+ Unit cell     79.343 79.343 38.121 90.000 90.000 90.000
+ Resolution    1.69 A written; the CC1/2 fall-off is fitted at 1.72 A
+ Completeness  100.0 % to 1.79 A; 98.4 % over the full written range
+ Signal        I/sigma 12.8   CC1/2 0.978
+ Files         sacla236.cif sacla236.hkl sacla236.mtz sacla236_blobs.json
+               sacla236_log.txt sacla236_maps.mtz sacla236_model.cif
+               sacla236_model.pdb sacla236_module_placement.json
+               sacla236_modules.h5 sacla236_plot.txt sacla236_refined_maps.mtz
+               sacla236_refined_model.cif sacla236_refined_model.pdb
+               sacla236_report.txt sacla236_unmerged.mtz
+ Wall time     34.64 s
+```
+
+Both warnings are expected here. The deposited model was refined against these reflections, so the
+free set drawn by this run is not truly free. A few percent of the reflections hold a saturated
+pixel. About 95 % of the 2424 frames are indexed and the refined model has an R-free of about 0.17.
+For serial data `sacla236_report.txt` gives `R_SPLIT` and `CC_HALF_SPLIT` (one half of the frames
+against the other) in place of R_meas. `sacla236_module_placement.json` records where each panel
+was placed.
 
 ## Your own data