scripts/sphinx-pre-install: fix Arch latexmk dependency

On Arch Linux, latexmk is installed in the texlive-core package.
Signed-off-by: Louis Taylor <louis@kragniz.eu>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

scripts/sphinx-pre-install

@@ -520,6 +520,7 @@ sub give_arch_linux_hints()
 		"dot"			=> "graphviz",
 		"convert"		=> "imagemagick",
 		"xelatex"		=> "texlive-bin",
+		"latexmk"		=> "texlive-core",
 		"rsvg-convert"		=> "extra/librsvg",
 	);