[jpaine]

README-only changes:

1. Cron example — Removed the duplicate cron block under Use cases; kept the single example under Self-hosting → Using cron, with a short pointer from the use case.
2. Custom domains — Stated the hard limit: only *.beehiiv.com subdomains; custom domains are not supported (removed the markup hedge).
3. React Native snippet — Uses rss-parser and parser.parseString() instead of an unnamed parse().