Update the help text for the "file existence check" option

This option actually controls whether the disk will be queried for the current file size and modification date/time (when listing) too.

src/sbbs3/scfg/scfgxfr2.c

@@ -1504,7 +1504,8 @@ void dir_cfg(uint libnum)
 									"`Check for File Existence When Listing:`\n"
 									"\n"
 									"If you want the actual existence of files to be verified while listing\n"
-									"directories, set this value to `Yes`.\n"
+									"directories and to have the current file size and modification time\n"
+									"reported when listing files, set this value to `Yes`.\n"
 									"\n"
 									"Directories with files located on CD-ROM or other slow media should have\n"
 									"this option set to `No`.\n"