You should copy .service to /etc and edit username or create ircd user. Probably postinstall message is needed....

i tried this:

$ systemctl enable unrealircd
ln -s '/usr/lib/systemd/system/unrealircd.service' '/etc/systemd/system/multi-user.target.wants/unrealircd.service'
$ useradd ircd
$ chown -R ircd:ircd /etc/unrealircd/
$ systemctl start unrealircd
Job for unrealircd.service failed.
$ journalctl -xn
-- Logs begin at Fri 2013-08-09 13:37:12 CEST, end at Wed 2013-08-21 13:41:09 CEST. --
Aug 21 13:41:09 niki unrealircd[15965]: using zlib 1.2.8
Aug 21 13:41:09 niki unrealircd[15965]: using libcurl/7.32.0 OpenSSL/1.0.1e zlib/1.2.8 libssh2/1.4.3
Aug 21 13:41:09 niki unrealircd[15965]: * Loading IRCd configuration ..
Aug 21 13:41:09 niki unrealircd[15965]: * Configuration loaded without any problems ..
Aug 21 13:41:09 niki unrealircd[15965]: * Initializing SSL.
Aug 21 13:41:09 niki unrealircd[15965]: * Dynamic configuration initialized .. booting IRCd.
Aug 21 13:41:09 niki unrealircd[15965]: ---------------------------------------------------------------------
Aug 21 13:41:09 niki systemd[1]: unrealircd.service: control process exited, code=exited status=9
Aug 21 13:41:09 niki systemd[1]: Failed to start IRC daemon.
-- Subject: Unit unrealircd.service has failed

you need to adjust config. It is shipped with an example config.

$ unrealircd
_ _ _ ___________ _____ _
| | | | | |_ _| ___ \/ __ \ | |
| | | |_ __ _ __ ___ __ _| | | | | |_/ /| / \/ __| |
| | | | '_ \| '__/ _ \/ _` | | | | | / | | / _` |
| |_| | | | | | | __/ (_| | |_| |_| |\ \ | \__/\ (_| |
\___/|_| |_|_| \___|\__,_|_|\___/\_| \_| \____/\__,_|
v3.2.10.1
using TRE 0.8.0 (BSD)
using OpenSSL 1.0.1e 11 Feb 2013
using zlib 1.2.8
using libcurl/7.32.0 OpenSSL/1.0.1e zlib/1.2.8 libssh2/1.4.3

* Loading IRCd configuration ..
[error] unrealircd.conf:587: tld::motd: ircd.motd.fr: No such file or directory
[error] unrealircd.conf:588: tld::rules: ircd.rules.fr: No such file or directory
[error] unrealircd.conf:771: set::cloak-keys: (key 2) Keys should be mixed a-zA-Z0-9, like "a2JO6fh3Q6w4oN3s7"
[error] unrealircd.conf:772: set::cloak-keys: (key 3) Keys should be mixed a-zA-Z0-9, like "a2JO6fh3Q6w4oN3s7"
[error] unrealircd.conf:769: set::cloak-keys: All your 3 keys should be RANDOM, they should not be equal
[error] unrealircd.conf:789: set::kline-address must be an e-mail or an URL
[error] 6 errors encountered
[error] IRCd configuration failed to pass testing

well ok, it's working as root :/

$ unrealircd
WARNING: You are running UnrealIRCd as root and it is not
configured to drop priviliges. This is _very_ dangerous,
as any compromise of your UnrealIRCd is the same as
giving a cracker root SSH access to your box.
You should either start UnrealIRCd under a different
account than root, or set IRC_USER in include/config.h
to a nonprivileged username and recompile.
_ _ _ ___________ _____ _
| | | | | |_ _| ___ \/ __ \ | |
| | | |_ __ _ __ ___ __ _| | | | | |_/ /| / \/ __| |
| | | | '_ \| '__/ _ \/ _` | | | | | / | | / _` |
| |_| | | | | | | __/ (_| | |_| |_| |\ \ | \__/\ (_| |
\___/|_| |_|_| \___|\__,_|_|\___/\_| \_| \____/\__,_|
v3.2.10.1
using TRE 0.8.0 (BSD)
using OpenSSL 1.0.1e 11 Feb 2013
using zlib 1.2.8
using libcurl/7.32.0 OpenSSL/1.0.1e zlib/1.2.8 libssh2/1.4.3

* Loading IRCd configuration ..
* Configuration loaded without any problems ..
* Initializing SSL.
* Dynamic configuration initialized .. booting IRCd.
---------------------------------------------------------------------

$ ps aux | grep unreal
root 30608 0.0 0.0 33284 3304 ? S 14:33 0:00 unrealircd

Added .install file with instructions