Disable systemd-resolve breaks DNS resolution

Good morning,

I'm curently following this tutorial to setup an ADblocker DNS server on my VPS
https://github.com/ragibkl/adblock-dns-server

On the step where I need to verify if the port 53 is available with `# lsof -i:53`, it says that `systemd-resolved` is currently using it, so I'm following the steps given :
- Disable and stop `systemd-resolve`
- Edit `/etc/resolv.conf` to add two lines `nameserver` with the DNS i want

But it seems there's already a configuration setup at `/etc/resolv.conf`
```
nameserver 127.0.0.53
options edns0
search openstacklocal
```
But when commenting the current configuration, and adding my two nameservers, the DNS resolution breaks.

Thanks for your help,