update readme

Signed-off-by: Jakub Sokołowski <jakub@status.im>

ansible/roles/nimbus-stats/README.md

@@ -2,6 +2,52 @@
 
 This role defined a simple service which lists the current state of the nodes in the fleet.
 
+# Configuration
+
+The only setting that should be usually changed is the domain:
+```yaml
+nimbus_stats_domain: my-amazing-domain.example.org
+```
+
+# Script
+
+The [`collect.py`](./files/collect.py`) script queries ElasticSearch for the logs we want to publish.
+
+This script is by default put under `/usr/local/bin/collect_nimbus_stats.py` and is used by the `/usr/local/bin/save_nimbus_stats.py` in a `cron` job.
+```
+Usage: collect.py [options]
+
+This script collects latest log entries for provided messages from all nodes
+in a Nimbus fleet
+
+Options:
+  -h, --help            show this help message and exit
+  -i ES_INDEX, --index=ES_INDEX
+                        Patter for matching indices. (logstash-2019.04.18)
+  -m MESSAGES, --messages=MESSAGES
+                        Messages to query for. (['Fork chosen', 'Attestation
+                        received', 'Slot start'])
+  -H ES_HOST, --host=ES_HOST
+                        ElasticSearch host. (localhost)
+  -P ES_PORT, --port=ES_PORT
+                        ElasticSearch port. (9200)
+  -p PROGRAM, --program=PROGRAM
+                        Program to query for. (*beacon-node-*)
+  -s SINCE, --since=SINCE
+                        Period for which to query logs. (now-30m)
+  -S PAGE_SIZE, --page-size=PAGE_SIZE
+                        Size of results page. (10000)
+  -f FLEET, --fleet=FLEET
+                        Fleet to query for. (nimbus.test)
+  -l LOG_LEVEL, --log-level=LOG_LEVEL
+                        Logging level. (INFO)
+  -o OUTPUT_FILE, --output-file=OUTPUT_FILE
+                        File to which write the resulting JSON.
+
+Example: collect -i logstash-2019.03.01 output.json
+```
+
 # Context
 
 For more details see: https://github.com/status-im/infra-nimbus/issues/1
+