chore: Add example to go readme. (#186)

## Summary

Adds a basic example to the readme.

## How did you test this change?

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Author: kinyoklion

go/README.md

@@ -17,9 +17,30 @@ go get github.com/launchdarkly/observability-sdk/go
 Install the plugin when configuring your LaunchDarkly SDK.
 
 ```go
-// TODO: Add code sample for Go observability plugin configuration
+import (
+	ld "github.com/launchdarkly/go-server-sdk/v7"
+	"github.com/launchdarkly/go-server-sdk/v7/ldplugins"
+	ldobserve "github.com/launchdarkly/observability-sdk/go"
+)
+
+func main() {
+	client, _ := ld.MakeCustomClient(os.Getenv("LAUNCHDARKLY_SDK_KEY"),
+		ld.Config{
+			Plugins: []ldplugins.Plugin{
+				ldobserve.NewObservabilityPlugin(
+					ldobserve.WithEnvironment("test"),
+					ldobserve.WithServiceName("go-plugin-example"),
+					ldobserve.WithServiceVersion(version.Commit),
+				),
+			},
+		}, 5*time.Second)
+
+		// Implementation specific code.
+}
 ```
 
+Example applications are available here: https://github.com/launchdarkly/observability-sdk/tree/main/e2e/go-plugin
+
 LaunchDarkly overview
 -------------------------
 [LaunchDarkly](https://www.launchdarkly.com) is a feature management platform that serves trillions of feature flags daily to help teams build better software, faster. [Get started](https://docs.launchdarkly.com/home/getting-started) using LaunchDarkly today!