Add a 'preprint' watermark

ICHLL_Brenon.md

@@ -16,6 +16,7 @@ header-includes:
 	- \usepackage{hyperref}
 	- \usepackage{geometry}
 	- \geometry{margin=25.4mm}
+	- \usepackage[text=preprint,fontsize=0.2\paperwidth,colorspec=0.9]{draftwatermark}
 	- \hypersetup{
 	        colorlinks,
 	        linkcolor = blue,