docs(mimic-iv): sample eMAR search for Vitamin C

Complement prescriptions when studying administered exposure (#1962).

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

Author: Chessing234

mimic-iv/concepts/documentation/vitamin_c_emar.sql

@@ -0,0 +1,10 @@
+-- Candidate Vitamin C administrations in emar (#1962).
+
+SELECT medication, COUNT(*) AS n
+FROM hosp.emar
+WHERE LOWER(medication) LIKE '%ascorbic%'
+   OR LOWER(medication) LIKE '%vitamin c%'
+   OR LOWER(medication) LIKE '%vit c%'
+GROUP BY medication
+ORDER BY n DESC
+LIMIT 50;