Update documentation.

README.md

@@ -16,6 +16,8 @@ This project is in active use by [telegram-bot.app](https://telegram-bot.app), a
   - [Speed](#speed)
     - [Caching](#caching)
     - [Read-only endpoint](#read-only-endpoint)
+  - [Maintenance](#maintenance)
+    - [Hasura event cleaner](#hasura-event-cleaner)
   - [Security](#security)
     - [Role-based rate limiting](#role-based-rate-limiting)
     - [Read-only mode](#read-only-mode)
@@ -175,6 +177,12 @@ You can now specify the read-only GraphQL endpoint by setting the `HOST_GRAPHQL_
 
 You can check out the [example of combined deployment with RW and read-only hasura](static/kubernetes-single-deployment-with-ro.yaml).
 
+### Maintenance
+
+#### Hasura event cleaner
+
+When enabled via `HASURA_EVENT_CLEANER=true` - proxy needs to have a direct access to the database to execute simple delete queries on schedule. You can specify number of days the logs should be kept for using `HASURA_EVENT_CLEANER_OLDER_THAN`, for example `HASURA_EVENT_CLEANER_OLDER_THAN=14` will keep 14 days of event execution logs. Ticker managing the cleaner routine will be executed every hour.
+
 ### Security
 
 #### Role-based rate limiting