user/chrony: add pidfile to .conf file

This is necessary for the OpenRC script to function.

user/chrony/chrony.conf

@@ -8,3 +8,6 @@ rtcsync
 # check /etc/conf.d/chrony if you want daemon logs to go to syslog
 # this setting specifies where statistics go
 logdir /var/log/chrony
+
+# Needed for the OpenRC script to work correctly
+pidfile /var/run/chronyd.pid