Add README

README.md

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 # kafka-hawk
-An application that records stats about consumer group offset commits and reports them as prometheus metrics
+
+An application that records stats about consumer group offset commits and
+reports them as prometheus metrics.
+
+This application is useful for determining how frequently each consumer group
+in your Kafka cluster is committing the offsets and, for the chattiest ones,
+it can calculate what the offset deltas are over time.
+
+## Deployment
+
+This application is packaged and designed to be deployed using a Docker image.
+It's available on Docker Hub as `farmdawgnation/kafka-hawk`.
+
+## Configuration
+
+The application can be configured by environment variables for most cases.
+
+* `BOOTSTRAP_SERVERS` — (required) The bootstrap servers setting for hawk
+* `GROUP_ID` - (optional) The group id, defaults to "hawk"
+* `SASL_CONFIG` - (optional) The SASL config if needed
+
+The application also has an optional feature that can report on the offset
+commit deltas. You have to enable this per consumer group because it requires
+more resources to track the offset diffs in memory. It can be enabled with
+and configured with the following environment variables:
+
+* `FEATURES_DELTAS_ENABLED` - Set to "true" to enable the feature
+* `FEATURES_DELTAS_GROUPS` - A comma separated list of groups to report deltas on
+
+# About the Author
+
+This tool was written by Matt Farmer who by day slings code and architecture
+for [Mailchimp](https://mailchimp.com)'s Data Application Development Team.