docs: improve diagnostics user journey

pages/diagnostics/user-journey.md

@@ -1,12 +1,35 @@
 # User Journey
 
-These diagnostics guides were created by the [Diagnostics Working Group][]
-and the [Node.js Website Team][] with the objective of providing guidance
-when diagnosing an issue in a user's application.
+Diagnostics is the process of collecting and analyzing information about an
+application to identify the cause of unexpected behavior, memory problems, or
+poor performance. These guides organize that process around common symptoms
+and link to tools and techniques that can help investigate them.
 
-The documentation project is organized based on user journey. Those journeys
-are a coherent set of step-by-step procedures that a user can follow to
-root-cause their issues.
+## Before you begin
+
+Record the following information before starting an investigation:
+
+- The Node.js version and operating system
+- The observed symptoms and when they occur
+- The steps needed to reproduce the problem
+- Recent changes to the application or its environment
+
+## Choose a diagnostic path
+
+Start with the guide that most closely matches the symptoms:
+
+- For incorrect or unexpected application behavior, see
+  [Live Debugging](/learn/diagnostics/live-debugging).
+- For increasing memory use, out-of-memory crashes, or frequent garbage
+  collection, see [Memory](/learn/diagnostics/memory).
+- For high latency or CPU usage, see
+  [Poor Performance](/learn/diagnostics/poor-performance).
+
+Each guide provides more specific symptoms and links to the relevant diagnostic
+tools and techniques.
+
+These guides were created by the [Diagnostics Working Group][] and the
+[Node.js Website Team][].
 
 [Diagnostics Working Group]: https://github.com/nodejs/diagnostics
 [Node.js Website Team]: https://github.com/nodejs/nodejs.org