notifier: add README

notifier/README.md

@@ -0,0 +1,26 @@
+# Notifications
+
+Notifications are a way for Clair to inform an endpoint that changes to tracked vulnerabilities have occurred.
+Notifications should contain only the name of a notification.
+Because notification data can require pagination, it is expected that the receiving endpoint calls the Clair API for reading notifications and marking them as read after being notified.
+
+## Webhook
+
+Webhook is an out-of-the-box notifier that sends the following JSON object via an HTTP POST:
+
+```json
+{
+  "Notification": {
+    "Name": "6e4ad270-4957-4242-b5ad-dad851379573"
+  }
+}
+```
+
+## Custom Notifiers
+
+Clair can also be compiled with custom notifiers by importing them in `main.go`.
+Custom notifiers are any Go package that implements the `Notifier` interface and registers themselves with the `notifier` package.
+Notifiers are registered in [init()] similar to drivers for Go's standard [database/sql] package.
+
+[init()]: https://golang.org/doc/effective_go.html#init
+[database/sql]: https://godoc.org/database/sql