Consolidating duplicate information and adding links to QuantEcon.site README

@jstac Proposed updates to README files. 

This consolidates the list of developers and project coordinators to the website repo. I have also removed the main references to the ``QuantEcon`` Course website and added it as a link under ``Additional Links`` along with developers and coordinators. 

I have added what will be the library website address. 

The rest should be reasonably ``python`` / ``julia`` specific and I think it is helpful to have the install instructions in the README of each relevant repository. 

I have left the License in the README as it shouldn't really change. But let me know if you want it removed.