Add README.md

Adding initial instructions for installing the re-design prototype with Nektar++. Currently missing information for installing with CUDA support, see #6 (closed).

README.md

+# How to install redesign-prototye
+## Build Nektar++ e.g. on current master
+- See README.md under [Nektar++ repository](https://gitlab.nektar.info/nektar/nektar)
+- For development, the `Debug` option is recommended
+- Note that the SIMD options have to be turned off, if you want to use CUDA support (Should be by default).
+
+## Build Nektar++ redesign-prototype
+In main directory of the redesign, create a `build` directory `cd` into it, configure and build via:
+```bash
+mkdir build
+cd build
+cmake ../ -DNektar++_DIR=~/code/nektarMaster/build/dist/lib64/nektar++/cmake -DCMAKE_BUILD_TYPE=Debug
+make 
+```
+
+If boost is not available on system, build boost (e.g. v1.71.1)
+- One option is via the Ubuntu package manager `sudo apt install libboost-all-dev`
+- Another option is to download boost and install it manually
+
+After installing boost, run again:
+```bash
+cmake ../ -DNektar++_DIR=~/code/nektarMaster/build/dist/lib64/nektar++/cmake -DCMAKE_BUILD_TYPE=Debug
+make
+```
+
+When the installation was successful, check it via tests:
+```bash
+ctest --output-on-failure
+```
+
+## Build Nektar++ redesign-prototype with CUDA
+To build the redesign project with CUDA:
+- The CUDA option must be turned on
+- The SIMD option must be turned off
+
+This can be obtained by using the following command
+```bash
+cmake ../ -DNektar++_DIR=~/code/nektarMaster/build/dist/lib64/nektar++/cmake -DCMAKE_BUILD_TYPE=Debug -DNEKTAR_USE_CUDA=ON -DNEKTAR_USE_SIMD=OFF 
+make
+```