update help doc for --diff-style so it shows correct options

[joannecheng]

Fixes #429

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.60%. Comparing base (bcac26f) to head (66871cf).
⚠️ Report is 10 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #465   +/-   ##
=======================================
  Coverage   74.60%   74.60%           
=======================================
  Files          52       52           
  Lines        2827     2827           
  Branches      286      286           
=======================================
  Hits         2109     2109           
  Misses        522      522           
  Partials      196      196           

Flag	Coverage Δ
integration	54.22% <100.00%> (ø)
unit	69.29% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 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.