Add an "install accessories" script

[recursion-ninja]

PCG outputs several data files intended to be consumed by other programs. It would be very nice for the users if we had a script to install all these utilities for them.

Some nice packages/programs to include would be:

• graphviz
• lapack
• gmplib
• stdc++

[Boarders]

Since this issue was mentioned when I suggested that nix gives one (relatively easy) approach to this kind of issue I should mention here that this can be done in nix via the command (though I don't recommend global installs like this):

nix-env --install graphviz liblapack gmp gcc

Alternatively one can create a fresh shell environment where each of these packages are installed (but not installed globally) via:

nix-shell --packages graphviz liblapack gmp gcc

This might be useful knowledge for quick testing purposes to create an environment with these installed.