build.sh: Add basic usage

Signed-off-by: Petr Vorel <pvorel@suse.cz>

build.sh

@@ -174,14 +174,28 @@ print_log()
 	echo "=== END $log ==="
 }
 
+usage()
+{
+	cat << EOF
+Usage:
+$0 [ build|build-log|check-binaries|configure|dependencies|dist|info|install|install-log|test|test-log ]
+$0 { -h|--help|help }
+
+EOF
+}
+
 cd `dirname $0`
 
 cmd=
 case "${1:-}" in
-	build|build-log|check-binaries|configure|dependencies|dist|info|install|install-log|test|test-log|"") cmd="${1:-}";;
+	-h|--help|help|build|build-log|check-binaries|configure|dependencies|dist|info|install|install-log|test|test-log|"") cmd="${1:-}";;
 	*) echo "ERROR: wrong command '$1'" >&2; exit 1;;
 esac
 
+if [ "$cmd" = "help" -o "$cmd" = "--help" -o "$cmd" = "-h" ]; then
+	usage
+fi
+
 if [ -z "$cmd" -o "$cmd" = "dependencies" ]; then
 	check_build_dependencies
 fi