Updating build instructions to include BLAS support (#1183)

Updating build instructions to include BLAS support (#1183)

* Updated build information

First update to the build instructions to include BLAS.

* Update README.md

* Update information about BLAS

* Better BLAS explanation

Adding a clearer BLAS explanation and adding a link to download the CUDA toolkit.

* Better BLAS explanation

* BLAS for Mac

Specifying that BLAS is already supported on Macs using the Accelerate Framework.

* Clarify the effect of BLAS

* Windows Make instructions

Added the instructions to build with Make on Windows

* Fixing typo

* Fix trailing whitespace