Update README.md Instructions

[jordantrizz]

I spent a half hour trying to figure out what the right combination of settings would send the correct information to the Cloudflare Worker. This is what worked for me.

• Server: dyndns
• Hostname: host.domain.com
• Username: domain.com
• Password: cloudflare-token
• Server: home-ddns.workerorg.workers.dev/update?ip=%i&hostname=%h

This works with a UDM Pro on 4.0.21

When using custom, the following occurs.

1. You can't use https:// in the server section
2. Anything in the server after the hostname is added to the config as the name of the service and fails to start.
3. Once you set server to "home-ddns.workerorg.workers.dev" it just sends the following requests

GET https://home-ddns.workersorg.workers.dev/updatehost.domain.com

I think you could probably update the README.md to include the above information and save some people time.