Add guided running stats explorer with validated queries and comparisons

README.md

@@ -47,6 +47,20 @@ migrations. SQLite and deployed PostgreSQL migrations have been verified; see
 - Routes are not masked or trimmed. Access control, rather than geographic masking,
   determines who can see the full route, including start and finish.
 
+### Exploring running stats
+
+Open **Stats** for the guided question builder: select up to two metrics, filter
+by distance and run-average heart rate, group by week or month, and compare an
+equally long preceding period. Periods use your account timezone and end today
+unless you choose an end date. The explorer covers whole runs and uses persisted
+summaries without loading recording samples. Metric definitions and the number
+of runs with usable data appear alongside each result.
+
+**Show query** exposes the same question as an editable DSL. Applying it updates
+the guided controls. Select a chart point or use the evidence period picker to
+inspect contributing runs. Save named views in this browser, or bookmark the
+results URL; saved views follow relative dates as new runs are imported.
+
 ### Bringing in more activities
 
 Use **Settings & imports -> Connect Garmin** to upload an exported session, then