Update INSTALL-Linux.markdown

During the bootstrap it launched me this errors:

Use of uninitialized value in pattern match (m//) at /usr/bin/autoreconf line 196.
autoreconf: Entering directory `.'
autoreconf: configure.ac: not using Gettext
autoreconf: running: aclocal --force -I m4
aclocal: couldn't open directory `m4': El fitxer o directori no existeix
autoreconf: aclocal failed with exit status: 1

I needed to install libtool and create the directory m4 inside the root of the folder to adress those issues.