Add package xparse (#31)

The package xparse should be included since
\NewDocumentCommand is part of it

lkmpg.tex

@@ -4,6 +4,7 @@
 \usepackage[T1]{fontenc}
 \usepackage{graphicx}
 \usepackage{fancyhdr}
+\usepackage{xparse}
 
 % tikz settings
 \usepackage{tikz}