Add README

README.md

+# elixxir/gpumathsnative
+
+## Building the native gpumaths library
+
+Before beginning, install the CUDA toolkit, version 10.2 and libgmp-dev.
+
+```
+$ wget https://developer.download.nvidia.com/compute/cuda/repos/ubuntu1804/x86_64/
+cuda-ubuntu1804.pin
+$ sudo mv cuda-ubuntu1804.pin /etc/apt/preferences.d/cuda-repository-pin-600
+$ wget http://developer.download.nvidia.com/compute/cuda/10.2/Prod/local_installers/
+cuda-repo-ubuntu1804-10-2-local-10.2.89-440.33.01_1.0-1_amd64.deb
+$ sudo dpkg -i cuda-repo-ubuntu1804-10-2-local-10.2.89-440.33.01_1.0-1_amd64.deb
+$ sudo apt-key add /var/cuda-repo-10-2-local-10.2.89-440.33.01/7fa2af80.pub
+$ sudo apt-get update
+$ sudo apt-get -y install cuda
+```
+
+```
+$ sudo apt install libgmp-dev
+```
+
+Next, build and install the native gpumaths library. You must have nvcc in your PATH for this to work.
+
+```
+$ cd cgbnBindings/powm
+$ make turing
+$ sudo make install
+```
+
+Then, you should be able to build the server with GPU support.
+