docs(spp_metric_service): re-render README for the amended HISTORY entry

Author: gonzalesedwin1123

spp_metric_service/README.rst

@@ -120,7 +120,10 @@ Changelog
 
 - feat: demographic breakdown expansion and SQL column support for
   metric disaggregation (re-land from #76; uses the spp_cel_domain SQL
-  CASE compiler).
+  CASE compiler). Expansion is all-or-nothing: any individuals-scoped
+  dimension expands the whole registrant set to active members, so
+  breakdown totals count members and need not reconcile with a
+  group-level scope count.
 
 19.0.2.0.0
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