docs: add workflow benefit line for Web UI section

"Review all visual changes in one place" — explains WHY developers
should use the Web UI, not just WHAT it does.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: pftg

README.md

@@ -114,7 +114,7 @@ After tests run, open `doc/screenshots/snap_diff_report.html`:
 
 ![SnapDiff Web UI — side-by-side comparison with baseline and current screenshots](docs/images/snap_diff_web_ui.png)
 
-4 view modes (both/base/new/heatmap), per-image zoom, annotation toggle, keyboard navigation, and search.
+Review all visual changes in one place — no need to hunt through `.diff.png` files. 4 view modes (both/base/new/heatmap), per-image zoom, annotation toggle, keyboard navigation, and search.
 
 **In GitHub Actions**, the report renders inline as a CI artifact — no download needed. Add a PR comment with a link to the report automatically: