docs: track needs try (#133)

README.md

@@ -91,12 +91,15 @@ let messageValue = messageFlag.value
 ### Tracking events
 The Confidence instance offers APIs to track events, which are uploaded to the Confidence backend:
 ```swift
-confidence.track(eventName: "MyEvent", data: ["field": ConfidenceValue(string("value"))])
+try confidence.track(eventName: "MyEvent", data: ["field": ConfidenceValue(string("value"))])
 ```
 
 The SDK takes care of storing events in case of offline and retries in case of transient failures.
 
-It's also possible to set context data to be appended to all tracked events:
+Note that the data struct can't contain the key `context`, as that is reserved for entries set via `putContext` (see below):
+violating this rule will cause the track function to throw an error.
+
+To set context data to be appended to all tracked events:
 ```swift
 confidence.putContext(context: ["os_version": ConfidenceValue(string: "17.0")])
 ```