docs(js): Update tracing docs for react-router framework (#13817)

closes getsentry/sentry-javascript#16363

Author: chargome

platform-includes/performance/configure-sample-rate/javascript.react-router.mdx

@@ -1,21 +1,39 @@
-```javascript
+To enable automatic tracing you need to update the configuration of your client and server instrumentation:
+- For client-side tracing, include the `reactRouterTracingIntegration` to your integrations array.
+- Additionally you need to set the `tracesSampleRate` in your `Sentry.init()` calls.
+
+```javascript {tabTitle:Client} {filename:entry.client.tsx} {7,11}
 import * as Sentry from "@sentry/react-router";
 
 Sentry.init({
   dsn: "___PUBLIC_DSN___",
 
-  // This enables automatic instrumentation (highly recommended),
-  // but is not necessary for purely manual usage
-  // If you only want to use custom instrumentation:
-  // * Remove the `reactRouterTracingIntegration` integration
-  // * add `Sentry.addTracingExtensions()` above your Sentry.init() call
+  // This enables automatic instrumentation for client-side navigations
   integrations: [Sentry.reactRouterTracingIntegration()],
 
   // We recommend adjusting this value in production, or using tracesSampler
   // for finer control
   tracesSampleRate: 1.0,
-
+  
   // Set `tracePropagationTargets` to control for which URLs trace propagation should be enabled
   tracePropagationTargets: ["localhost", /^https:\/\/yourserver\.io\/api/],
+
+  // ... rest of your config
+});
+
+// ... rest of the file
+```
+
+```javascript {tabTitle:Server} {filename:instrument.server.(mjs|ts)} {8}
+import * as Sentry from "@sentry/react-router";
+
+Sentry.init({
+  dsn: "___PUBLIC_DSN___",
+
+  // We recommend adjusting this value in production, or using tracesSampler
+  // for finer control
+  tracesSampleRate: 1.0,
+
+  // ... rest of your config
 });
 ```