Install guide tweaks

This should close #2999 
> A reduction in the size of the current installers. The Anaconda installers were becoming too big, due to the inclusion of some large packages. These packages have been removed from the installers, but are still supported and available in the repository, meaning you can still use conda to install them. These packages include mayavi, netcdf4, vtk, and 10 others.

It looks like they have done some thing about that already, but added miniconda link as well.