added autoconf to apt install requirements (RPi)

[sfinktah]

I found I needed autoconf/automake. It may be possible to avoid this by adjusting the timestamps of the related files, but simply installing it takes < 30 seconds, and avoid this and any future issues.

I also added sudo -s after the reboot (see previous commit), and changed the initial sudo su to sudo -s for consistency.

config.status: executing libtool commands
CDPATH="${ZSH_VERSION+.}:" && cd . && /bin/bash /home/pi/nexmon/buildtools/mpfr-3.1.4/missing aclocal-1.15 -I m4
/home/pi/nexmon/buildtools/mpfr-3.1.4/missing: line 81: aclocal-1.15: command not found
WARNING: 'aclocal-1.15' is missing on your system.
         You should only need it if you modified 'acinclude.m4' or
         'configure.ac' or m4 files included by 'configure.ac'.
         The 'aclocal' program is part of the GNU Automake package:
         <http://www.gnu.org/software/automake>

[conor-f]

This isn't fully complete. See #344 for details. Basically just also needs the packages texinfo, libtool-bin, and automake then run autoreconf -f -i in the mpfr directory. If I get time I'll just patch this onto this PR.

[baselsayeh]

@sfinktah
the source setup_env.sh script do not need root access

[sfinktah]

I fully appreciate that this was far from a ideal solution, but I thought it worth documenting some instructions that at least worked.

@baselsayeh I don't believe I added any root access that wasn't already in there, just changed su for sudo