[Minor] Support reload in systemd service file

rspamd.service

@@ -6,6 +6,7 @@ After=nss-lookup.target
 LimitNOFILE=1048576
 NonBlocking=true
 ExecStart=/usr/bin/rspamd -c /etc/rspamd/rspamd.conf -f
+ExecReload=/bin/kill -HUP $MAINPID
 User=_rspamd
 RuntimeDirectory=rspamd
 RuntimeDirectoryMode=0755