explicit what sslhconf.cfg is for

sslhconf.cfg

@@ -1,3 +1,9 @@
+# This is a configuration file for the configuration
+# generator: it is used by
+# conf2struct(http://www.rutschle.net/tech/conf2struct/README.html)
+# to generate the config file and command line parser in
+# sslh-conf.c
+
 header: "sslh-conf.h";
 parser: "sslh-conf.c";