docs: add program-desc to howto-usage-function.txt and boilerplate.c

Signed-off-by: Karel Zak <kzak@redhat.com>

Documentation/boilerplate.c

@@ -33,6 +33,10 @@ static void __attribute__((__noreturn__)) usage(FILE *out)
 {
 	fputs(USAGE_HEADER, out);
 	fprintf(out, _(" %s [options] file...\n"), program_invocation_short_name);
+
+        fputs(USAGE_SEPARATOR, out);
+        fputs(_("Short program description.\n"), out);
+
 	fputs(USAGE_FUNCTIONS, out);
 	fputs(_(" -s, --do-something      some specific task\n"), out);
 	fputs(_(" -o, --do-other          some different task\n"), out);

Documentation/howto-usage-function.txt

@@ -42,6 +42,8 @@ look like.
 Usage:
  program [options] <file> [...]
 
+Short program description, ideally one line only.
+
 Options:
  -n, --no-argument       option does not use argument
      --optional[=<arg>]  option argument is optional