Add link to Prometheus docs on 2.0 -> 3.0

docs/sources/mimir/release-notes/v2.15.md

@@ -56,7 +56,7 @@ The following alertmanager metrics are not exported for a `user` when the metric
 - `cortex_alertmanager_alerts`
 - `cortex_alertmanager_silences`
 
-PromQL compatibility has been upgraded from Prometheus 2.0 to 3.0. The following has changed as a result:
+PromQL compatibility has been upgraded from Prometheus 2.0 to 3.0. More details can be found in the [Prometheus documentation](https://prometheus.io/docs/prometheus/3.0/migration/#promql). The following changes are of note:
 
 - The `.` pattern in regular expressions in PromQL now matches newline characters.
 - Lookback and range selectors are left open and right closed (previously left closed and right closed).