Fix heading level

doc/self-hosters/domains.md

@@ -20,7 +20,7 @@ The hosts file is a straightforward way to map domain names to IP addresses on i
    192.168.1.10 api.puter.local
    ```
 
-### For macOS and Linux:
+#### For macOS and Linux:
 1. Open a terminal.
 2. Edit the hosts file with a text editor, e.g., `sudo nano /etc/hosts`.
 3. Add lines for your domain and subdomain with the server's IP address, in the