Add root README describing service topology

[Copilot]

This repo lacked a top-level README, making it harder for new contributors to understand what it contains. This change adds a concise root-level overview of the microservice app and its key directories.

• What was added

  • New /README.md at repository root
  • Brief description of the repo as a 4-service Node.js HTTP microservice sample

• Repository map

  • Documents roles of service1–service4
  • Calls out tests/service1-test.sh as the existing basic test script

• README content style

  • Kept intentionally short and scan-friendly for first-time readers
  • Focused on service responsibilities and repo layout only

# testapp

This repository contains a small Node.js microservices sample application made up of four services (`service1` through `service4`) that call each other over HTTP.