Yes, you can do this using a relative URL!
Here's how I wrote it:
[Here's an example.](/c/[email protected])
Because this URL doesn't have a protocol or a domain, your browser fills those in from the URL of the page you're on when you see it. Since that's on your local Lemmy instance, you'll see a link to [email protected] on that instance.
Also: When you're looking at a Lemmy comment, if you don't know how the author wrote the markup for it, you can use the "view source" button underneath the "..." menu.
Note: These links will NOT work between Lemmy and Kbin, because Kbin uses /m/
instead of /c/
.