Add documentation for using licenses for commercial dependencies

[jonrkarr]

CBMPy, COBRApy, MASSpy, and RBApy can run more quickly with commercial alternatives (e.g., Gurobi, CPLEX) to open-source dependencies (i.e. GLPK).

• CBMPy: CPLEX
• COBRApy: CPLEX or Gurobi
• MASSpy: CPLEX or Gurobi
• RBApy: CPLEX or Gurobi

Where possible, we recommend Gurobi because its available for a wider range of Python versions, its easier to download and install, its easier to get licenses, and the licenses are easier to use with Docker images.

Gurobi can be used in Docker images with a Web License Service for Container Environments Only. We've set up COBRApy and RBApy to read license keys from environment variables that start with the prefix "GRB_". MASSpy could be set up similarly. For use with GitHub actions, license keys could be stored as secrets.

CPLEX can also be installed alongside our simulation tools. We don't include CPLEX in our Docker images due to the way that it is licensed, which prevents us from redistributing it.

[jonrkarr]

Since this is handled by BioSimulators, Vivarium users just need documentation about how to use this.

For Gurobi, users should either

• Set environment variables with their license keys prefixed with GRB_ (e.g., GRB_TOKENSERVER for site licenses).
• Save their license keys to ~/gurobi.lic or the default OS location (e.g., /opt/gurobi/gurobi.lic for Linux)