`simula-openvr` lacks a nix expression

[georgewsinger]

Problem: After cloning Simula's master branch and running stack --nix build:

    Configuring simula-openvr-0.0.0...
    Cabal-simple_mPHDZzAJ_1.24.2.0_ghc-8.0.2: Missing dependency on a foreign
    library:
    * Missing C library: openvr_api
    This problem can usually be solved by installing the system package that
    provides this library (you may need the "-dev" version). If the library is
    already installed but in a non-standard location then you can use the flags
    --extra-include-dirs= and --extra-lib-dirs= to specify where it is.

Reason: simula-openvr lacks a nix expression.

[krakrjak]

This is fixed in https://github.com/SimulaVR/Simula/pull/15