Update INSTALL.md

Author: acontu

INSTALL.md

@@ -1,11 +1,19 @@
 Build application
 -------------------------------
+Make sure that you have the following packages available in your system:
+- [Hydra >= v2.2.1](https://github.com/MultithreadCorner/Hydra/releases/tag/v2.2.1)
+- [libconfig >= v1.5](https://github.com/hyperrealm/libconfig)
+- [TCLAP >= v1.2.1](http://tclap.sourceforge.net/)
+- [ROOT >= v6.14](https://root.cern.ch/)
 
+To generate executables to run on nVidia GPUs you also need an installation of [CUDA >= 8.1](https://developer.nvidia.com/cuda-toolkit) and to use a [compatible GCC version](https://docs.nvidia.com/cuda/).
+
+Build TCode following the instructions below:
 1. clone the git repository: `git clone https://github.com/MultithreadCorner/TCode.git`
 2. go to TCode directory: `cd TCode`
 3. create a build directory: `mkdir build` 
-4. cd build
-5. `cmake -DHYDRA_INCLUDE_DIR=<path-to-hydra>../`
-6. `make -j8`
+4. go to build directory cd `build`
+5. run cmake specifying the path to Hydra: `cmake -DHYDRA_INCLUDE_DIR='path-to-hydra'../`
+6. compile (all backends): `make -j8`
 
-Separate executables for CPP, TBB, OMP and CUDA backend will be produced (if available in your machine).
+Several executables, separate for each available backend (CPP, TBB, OMP and CUDA) will be generated.