tools.vet: print help when passing no files or --help/-help flag …

…after vet command (#21108)

cmd/tools/vvet/vvet.v

@@ -9,6 +9,7 @@ import v.pref
 import v.parser
 import v.token
 import v.ast
+import v.help
 import term
 
 struct Vet {
@@ -50,6 +51,9 @@ fn main() {
 		// `v test-cleancode` passes also `-o tmpfolder` as well as all options in VFLAGS
 		paths = paths.filter(!it.starts_with(vtmp))
 	}
+	if paths.len == 0 || '-help' in vet_options || '--help' in vet_options {
+		help.print_and_exit('vet')
+	}
 	for path in paths {
 		if !os.exists(path) {
 			eprintln('File/folder ${path} does not exist')