docs(js): Review and update Express Quick Start guide (#14218)

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Reviewed and updated the Express Quick Start guide.

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## EXTRA RESOURCES

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---------

Co-authored-by: Alex Krawiec <[email protected]>
Co-authored-by: Charly Gomez <[email protected]>

Author: 3 people

docs/platforms/javascript/guides/express/index.mdx

@@ -1,6 +1,6 @@
 ---
 title: Express
-description: "Learn about using Sentry with Express."
+description: "Learn how to manually set up Sentry in your Express app and capture your first errors."
 sdk: sentry.javascript.node
 fallbackGuide: javascript.node
 categories:
@@ -9,8 +9,4 @@ categories:
   - server-node
 ---
 
-<PlatformContent includePath="getting-started-primer" />
-
-This guide explains how to set up Sentry in your Express application.
-
 <PlatformContent includePath="getting-started-node" />

platform-includes/getting-started-node/javascript.mdx

@@ -72,14 +72,14 @@ Now, head over to your project on [Sentry.io](https://sentry.io/) to view the co
 
 ## Next Steps
 
-At this point, you should have integrated Sentry into your Node.js application and should already be sending data to your Sentry project.
+At this point, you should have integrated Sentry into your application, which should already be sending data to your Sentry project.
 
 Now's a good time to customize your setup and look into more advanced topics.
 Our next recommended steps for you are:
 
 - Extend Sentry to your frontend using one of our [frontend SDKs](/)
-- Learn how to [manually capture errors](/platforms/javascript/guides/node/usage/)
-- Continue to [customize your configuration](/platforms/javascript/guides/node/configuration/)
+- Learn how to <PlatformLink to="/usage">manually capture errors</PlatformLink>
+- Continue to <PlatformLink to="/configuration">customize your configuration</PlatformLink>
 - Get familiar with [Sentry's product features](/product) like tracing, insights, and alerts
 
 <Expandable permalink={false} title="Are you having problems setting up the SDK?">

platform-includes/getting-started-verify/javascript.express.mdx

@@ -1,5 +1,32 @@
+### Issues
+
+First, let’s make sure Sentry is correctly capturing errors and creating issues in your project. Add the following code snippet to your main application file; it defines a route that will deliberately trigger an error when called:
+
 ```javascript
 app.get("/debug-sentry", function mainHandler(req, res) {
   throw new Error("My first Sentry error!");
 });
 ```
+
+<OnboardingOption optionId="performance">
+
+### Tracing
+
+To test your tracing configuration, update the previous code snippet by starting a trace to measure the time it takes for the execution of your code:
+
+```javascript
+app.get("/debug-sentry", async (req, res) => {
+  await Sentry.startSpan(
+    {
+      op: "test",
+      name: "My First Test Transaction",
+    },
+    async () => {
+      await new Promise((resolve) => setTimeout(resolve, 100));
+      throw new Error("My first Sentry error!");
+    }
+  );
+});
+```
+
+</OnboardingOption>