improve DX of downloading external libraries

Since SYPC and Mimeparse have been removed, the DX of setting up the REST server has been degraded due to the necessity of finding, downloading and installing files from external libraries. The attached patch mitigates this by adding a pair of wget commands to the readme that will download the latest available versions of the required files. It's still less than optimal to require any user interaction to get REST Server working, but this will help to make the process less irritating.