diff --git a/ingestion/monitoring/README.md b/ingestion/monitoring/README.md
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--- a/ingestion/monitoring/README.md
+++ b/ingestion/monitoring/README.md
@@ -1,3 +1,20 @@
+# Error monitoring
+
+The `errorLogsToSlack.py` script reads log messages from a given Cloudwatch stream
+and posts any errors to Slack. It has three inputs, all passed via the environment:
+
+ - `SLACK_WEBHOOK` is the webhook URL to post messages to Slack.
+ - `INGESTION_LOG_GROUP` is the Cloudwatch log group name.
+ - `INGESTION_LOG_STREAM` is the Cloudwatch log stream name.
+
+Typically, all would be set up EventBridge in AWS when it's run in Batch.
+
+## To set up for a new instance
+
+1. see https://api.slack.com/messaging/webhooks for details on creating a Slack app and enabling web hooks.
+2. change the Slack user IDs in the script to ones that represent users in your workspace (who should get notified on ingestion errors).
+3. deploy to Batch
+
 # Data monitoring
 
 Data monitoring scripts, currently there's a script to alert daily about