Missing rar file related instructions for all operating systems #54
Description
As part of PR #53, the functionality for extracting rar files was added to the code base. The code checks if the user's operating system first can handle/unzip rar files before enacting the action. In the README, the PR adds a short instruction on how to install rar on macOS using brew. Instructions should be added for other operating systems as well, for users who would be interested in downloading the plexos-world-spatial model, which requires the extraction of a rar file.