docs(readme): Mark custom URL feature as completed in README

Author: jackseceng

readme.md

@@ -105,7 +105,7 @@ docker compose down
 - [x] Captcha on main page: Uses [Cloudflare Turnstile](https://www.cloudflare.com/en-gb/application-services/products/turnstile/)
 - [x] Static content served through CDN: Served via [Cloudflare R2](https://www.cloudflare.com/en-gb/developer-platform/products/r2/)
 - [x] Demonstration application set up: Hosted on [cloud.run](https://cloud.run)
-- [ ] Custom URLs users enter in the main form
+- [x] Custom URLs users enter in the main form
 - [x] Statistics page for URLs to see how many clicks links have got (go to `tld/url/stats` to see them)
 
 ## DevSecOps