fix: /metrics/history gives the availability of each site-to-site connection as the percentage of time it was up in slots of the view.

README.md

@@ -912,6 +912,17 @@ How it works:
   | `month` | 6 hours | hourly |
   | `year` | 1 month | monthly |
 
+- **Site-to-site availability:** `site_to_site_up` of the same answer divides the view into slots of its own, `slot`, and gives for each slot and connection the percentage of the samples in which the connection was up, 0 to 100, as `points` of `{"time", "connections": {name: percent}}`:
+
+  | Range | Slot | Source |
+  |---|---|---|
+  | `hour` | 5 minutes | details |
+  | `day` | 1 hour | details |
+  | `month` | 1 day | hourly |
+  | `year` | 1 month | monthly |
+
+  A sample is taken every minute, so an interruption shorter than a minute may be missed; a slot without samples has no value, and the year view, like the others of its level, has the complete months only.
+
 ### Scraping
 
 `GET /metrics` of the metrics service serves the last sample in the Prometheus text format, written by `prometheus_client`.