docs(mimic-iii): sample SpO2 pull for a stay list

Help validate #1957 cohorts before blaming missing pulse ox.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: Chessing234

mimic-iii/concepts/documentation/spo2_for_icustays.sql

@@ -0,0 +1,8 @@
+-- Template: SpO2 rows for a list of icustay_id values (both common itemids).
+
+SELECT ce.icustay_id, ce.itemid, ce.charttime, ce.valuenum, ce.valueuom
+FROM mimiciii.chartevents AS ce
+WHERE ce.itemid IN (646, 220277)
+  AND ce.icustay_id IN (/* your icustay_id list */)
+ORDER BY ce.icustay_id, ce.charttime
+LIMIT 100;