Added systemd module to support CentOS (#235)

Author: zishanj

httpd.conf

@@ -31,6 +31,12 @@ LoadModule autoindex_module modules/mod_autoindex.so
 LoadModule dir_module modules/mod_dir.so
 LoadModule rewrite_module modules/mod_rewrite.so
 
+# Enables Systemd module when available.
+# Required on some operating systems.
+# <IfFile modules/mod_systemd.so>
+#   LoadModule systemd_module modules/mod_systemd.so
+# </IfFile>
+
 <IfModule mod_unixd.c>
     # Run as a unique, less privileged user for security reasons.
     # User/Group: The name (or #number) of the user/group to run httpd as.