[Suggestion] Add a README which explains this repository

[jonrkarr]

I think it would be helpful to have a README which explains things such as:

• What kind of models are published here
• Where the model came from
• Where users should go to explore these models
  • https://biosimulations.org
  • https://vcell.org/vcell-published-models
• The file formats involved in this repository
• Which software can be used to execute the models in this repository
• The organization of this repository
• Licenses for the models -- see [Suggestion] Clarify that most of the content has no license, rather than the posted MIT license #1
• How to publish another model here
• How to suggest corrections to models
• Who created and maintains this repository