- make latexmk.pdf texdoc findable by installing it into /u/s/texmf/doc

hille@debian-amd64-sid:~/devel/TeXLive/git/github$ lintian -I --pedantic latexmk_4.75-2_all.deb
I: latexmk: possible-documentation-but-no-doc-base-registration
N: 3 hints overridden (3 info); 0 unused overrides
