add usage example to readme

README.md

@@ -1,5 +1,36 @@
-# package for sending events to Google Analytics 4 using the Measurement Protocol
+# ga4
+
+## package for sending events to Google Analytics 4 using the Measurement Protocol
 
 Measurement Protocol (Google Analytics 4) docs reference: https://developers.google.com/analytics/devguides/collection/protocol/ga4
 
-debugging tools: https://ga-dev-tools.google/ga4/event-builder/
+Debugging tools: https://ga-dev-tools.google/ga4/event-builder/
+
+### Usage
+
+```go
+package main
+
+import (
+    "fmt"
+    "github.com/ad/ga4"
+)
+
+func main() {
+    client := ga4.NewGA4Client("G-XXXXXXXXXX", "xxxxxxxxxxxxxxxxxxxxx", "", true)
+    err := client.SendEvent(
+        ga4.Event{
+            Name: "test_event",
+            Params: map[string]string{
+                "param1": "value1",
+                "param2": "value2",
+            },
+        },
+    )
+    if err != nil {
+        fmt.Println(err)
+    }
+}
+```
+
+