add preface template

main.tex

@@ -20,7 +20,8 @@
 \usepackage{graphicx}
 \usepackage{tikz}
 \graphicspath{{./images/}}
-
+% dependency graph
+\usetikzlibrary{positioning,arrows.meta}
 
 % --- Bibliography: biblatex + biber ---
 \usepackage[
@@ -71,6 +72,7 @@
 \mainmatter
 
 % Each chapter is in its own file and included as a subfile.
+\subfile{preface}
 \subfile{chapters/chap1}
 \subfile{chapters/chap2}
 \subfile{chapters/chap3}