Add link to OpenBSD packaging.

index.md

@@ -81,7 +81,7 @@ You can try it now using Docker:
 * On <a href="https://freebsd.org">FreeBSD</a> based systems:<br/>
 `pkg install py38-diffoscope`
 
-* On <a href="https://openbsd.org">OpenBSD</a> based systems:<br/>
+* On <a href="https://openbsd.org">OpenBSD</a> based systems (<a href="https://github.com/openbsd/ports/tree/master/sysutils/diffoscope">packaging</a>):<br/>
 `pkg_add diffoscope`
 
 * On <a href="https://nixos.org/">NixOS/nixpkgs</a>:<br/>`nix-shell -p diffoscope`