Document config wizard auto-detect and migration

[clcollins]

Summary

• Add note about auto-entering config wizard when no config file exists on first launch
• Document automatic migration from deprecated service_escalation_policies format

Test plan

• Verify README renders correctly on GitHub

🤖 Generated with Claude Code

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 65.34%. Comparing base (f2920e3) to head (a735687).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #295   +/-   ##
=======================================
  Coverage   65.34%   65.34%           
=======================================
  Files          35       35           
  Lines        5901     5901           
=======================================
  Hits         3856     3856           
  Misses       1791     1791           
  Partials      254      254           

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.