Document db index

deploy-guides/0001-eventlog-importing.md

@@ -58,6 +58,14 @@ on eventlog_import, heap_event, package
 to ghc_perf_web;
 ```
 
+### SQL indices
+
+This index was added to speed up the Eventlog Import Overview panel on Grafana.
+
+```sql
+create index heap_event_import_id_idx on heap_event (import_id);
+```
+
 ## Followup
 
 Here's a query that will inspect the output of the script: