RST: implement admonitions (#16438)

config/nimdoc.tex.cfg

@@ -52,6 +52,15 @@ doc.file = """
 \usepackage{hyperref}
 \usepackage{enumitem}
 
+\usepackage{xcolor}
+\usepackage[tikz]{mdframed}
+\usetikzlibrary{shadows}
+\mdfsetup{%
+linewidth=3,
+topline=false,
+rightline=false,
+bottomline=false}
+
 \begin{document}
 \title{$title $version}
 \author{$author}