Initial support for templating and instantiating services

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

doc/config.md

@@ -9,6 +9,7 @@ Finit Configuration
 * [Service Environment](#service-environment)
 * [Service Synchronization](#service-synchronization)
 * [Service Wrapper Scripts](#service-wrapper-scripts)
+* [Templating](#templating)
 * [Cgroups](#cgroups)
 * [Configuration File Syntax](#configuration-file-syntax)
   * [Hostname](#hostname)
@@ -353,6 +354,26 @@ example employs a wrapper script in `/etc/start.d`.
 >           instead of sending SIGHUP at restart/reload events.
 
 
+Templating
+----------
+
+Finit comes with rudimentary support for templating, similar to that of
+systemd.  Best illustrated with an example:
+
+      $ initctl show avahi-autoipd@
+      service :%i avahi-autoipd --syslog %i -- ZeroConf for %i
+
+To enable ZeroConf for, e.g., eth0, use
+
+      $ initctl enable avahi-autoipd@eth0.conf
+
+The enabled symlink will be set up to avahi-autoipd@.conf and every in‐
+stance of %i will in the instantiated directive be replaced with eth0.
+Inspect the result with:
+
+      $ initctl status avahi-autoipd:eth0
+
+
 Cgroups
 -------