Fix block comment syntax error from cron example

The */5 in the cron example inside the JSDoc block comment was parsed
as end-of-comment, causing a SyntaxError. Replaced with a reference
to install.sh.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

fetch-usage.js

@@ -17,8 +17,7 @@
  *
  * Output: Writes JSON to $CLAUDE_USAGE_CACHE or /tmp/claude_usage.json
  *
- * Cron example (every 5 min):
- *   */5 * * * * /usr/bin/node /path/to/fetch-usage.js 2>/dev/null
+ * Cron: every 5 min (see install.sh or README for crontab line)
  */
 const fs = require('fs');
 const path = require('path');