Enable RuleFolder by default

I don't really know why this was not enabled by default in the first
place but this is really useful, also to extend it with distro-specific
configuration without touching the upstream files themselves

usbguard-daemon.conf.in

@@ -24,7 +24,7 @@ RuleFile=%sysconfdir%/usbguard/rules.conf
 #
 # RuleFolder=/path/to/rulesfolder/
 #
-#RuleFolder=%sysconfdir%/usbguard/rules.d/
+RuleFolder=%sysconfdir%/usbguard/rules.d/