Update comment to suggest fallback to $XDG_CONFIG_HOME/hosts if HOSTS is unset

userhosts.c

@@ -60,7 +60,8 @@ static void __attribute__ ((constructor)) init(void) {
   original_fopen = dlsym_or_abort("fopen");
   replacement_hosts = getenv("HOSTS");
   if (!replacement_hosts)
-    /* XXX: warn ? fallback on $HOME/???/hosts ? */
+    /* IDEA: If HOSTS is not set, try $XDG_CONFIG_HOME/hosts
+     *       and maybe warn if the latter does not exist. */
     replacement_hosts = ORIGINAL_HOSTS_PATH;
 }