dependencies: pureos-trisquel: Add texlive-plain-generic for the website.

Without that fix we have the following issue when building a release:

    makeinfo \
    	 --pdf \
    	--no-split \
    	-o pages/manual/gnuboot.pdf \
    	../manual/gnuboot.texi
    This is pdfTeX, Version 3.141592653-2.6-1.40.22 [...]
    [...]
    Writing index file gnuboot.cp
    [1{/var/lib/texmf/fonts/map/pdftex/updmap/pdftex.map}] [2] [-1] Chapter 1
    ./../manual/gnuboot.texi:122: epsf.tex not found, images will be ignored.
    @image ...f.tex not found, images will be ignored}
    [...]
    ./../manual/gnuboot.texi:122: Emergency stop.
    @image ...f.tex not found, images will be ignored}
                                                      @global @warnednoepsftrue ...
    l.122 mainboard.}

    ./../manual/gnuboot.texi:122:  ==> Fatal error occurred, no output PDF file pro
    duced!
    [...]
    ./../manual/gnuboot.texi:122:  ==> Fatal error occurred, no output PDF file pro
    duced!
    Transcript written on gnuboot.log.
    /usr/bin/texi2dvi: pdfetex exited with bad status, quitting.
    make: *** [Makefile:767: pages/manual/gnuboot.pdf] Error 1

The epsf.tex can be found in the texlive-plain-generic package in
/usr/share/texlive/texmf-dist/tex/generic/epsf/epsf.tex.

This issue was introduced by the commit
08b9e449e9 ("Add a minimal GNU Boot
manual.").

Signed-off-by: Denis 'GNUtoo' Carikli <GNUtoo@cyberdimension.org>
Acked-by: Adrien 'neox' Bourmault <neox@gnu.org>

resources/dependencies/pureos-trisquel

@@ -134,7 +134,8 @@ install_packages \
     graphviz \
     pandoc \
     texinfo \
-    texlive
+    texlive \
+    texlive-plain-generic
 
 if [ -n "${to_install}" ] ; then
     apt install -y ${to_install}