Add Linux install instructions for Arch and Fedora

[subalterngames]

This issue is probably technically resolved in the sense that I can compile Cacophony on Debian and therefore I know that the feature flags aren't Ubuntu-specific.

I'm not familiar with Arch and Fedora. Can someone add install instructions for those distros (or for others) to the README?

[franciscod]

I haven't run the result in an actual Arch install, but this builds correctly as far as I can tell:

FROM archlinux:latest

RUN pacman -Syu --noconfirm \
      alsa-lib \
      clang \
      git \
      make \
      pkgconfig \
      rust \
      speech-dispatcher \
    ;

RUN git clone https://github.com/subalterngames/cacophony

RUN cd cacophony; cargo build
RUN cd cacophony; cargo build --release