Update README.md

README.md

@@ -286,6 +286,27 @@ Technically speaking Space is a mandatory field ("default" by default) on Functi
 to provide during function registration or subscription creation. Space is a first class concept in Config API. Config
 API can register function in specific space or list all functions or subscriptions from a space.
 
+## System Events
+
+System Events are special type of events emitted by the Event Gateway instance. They are emitted on each stage of event
+processing flow starting from receiving event to function invocation end. Those events are:
+
+* `gateway.event.received` - the event is emitted when an event was received by Events API. Data fields:
+  * `event` - event payload
+  * `path` - Events API path
+  * `headers` - HTTP request headers
+* `gateway.function.invoking` - the event emitted before invoking a function. Data fields:
+  * `event` - event payload
+  * `functionId` - registered function ID
+* `gateway.function.invoked` - the event emitted after successful function invocation. Data fields:
+  * `event` - event payload
+  * `functionId` - registered function ID
+  * `result` - function response
+* `gateway.function.invocationFailed` - the event emitted after failed function invocation. Data fields:
+  * `event` - event payload
+  * `functionId` - registered function ID
+  * `error` - invocation error
+
 ## APIs
 
 [API reference](./docs/api.md)