docs(claude-usage): mention <img> custom icon + list widget in README

[ManaphatDev]

Two small docs-only fixes for the Claude Usage widget (shipped in v2.0.3):

1. <img> custom icon note — in the widget's Placeholders section, document that the label can embed a custom image via an <img> tag, alongside the existing Nerd Font <span> glyph example.
2. README index — the widget was never added to the README widget list; add it alphabetically between Cava and Copilot.

No code changes.

[github-actions]

❌ Ruff Lint Check Failed

The code quality checks did not pass. Please review and fix the issues below:

📝 Format Issues

The following code needs formatting. Here are the differences:

--- src\core\widgets\yasb\volume.py
+++ src\core\widgets\yasb\volume.py
@@ -532,7 +532,13 @@
         widget_index = 0
 
         if self.volume is None:
-            fallback_icon = next(iter(self.config.icons.values())) if isinstance(self.config.icons, dict) else self.config.icons[0] if self.config.icons else ""
+            fallback_icon = (
+                next(iter(self.config.icons.values()))
+                if isinstance(self.config.icons, dict)
+                else self.config.icons[0]
+                if self.config.icons
+                else ""
+            )
             mute_status, icon_volume, level_volume = None, fallback_icon, "No Device"
             set_tooltip(self, "No audio device connected.")
         else:

1 file would be reformatted, 325 files already formatted

To fix: Run ruff format . in your local repository.

---

Note: The build will be skipped until these issues are resolved.
Please commit the fixes and push to this PR branch.

[ManaphatDev]

Heads-up: this PR only updates documentation (README.md + wiki page). The failing ruff format check is coming from volume.py, which is unchanged from main.

I'm happy to clean that up in a follow-up PR if that's preferred.

I also have a popup screenshot matching the current behavior on main if you'd like me to add a preview image to the wiki page.

[jondmarien]

Thanks @ManaphatDev. I've folded both of these into #973 and credited you via Co-Authored-By. They touch the same docs that PR rewrites, and keeping it to one PR is easier on the maintainer to review. The README list entry and the <img> note are both in there, so this is safe to close once #973 lands.