DOC: Update CUDA build overview

README.md

@@ -22,20 +22,12 @@ in Python, and are executed with `pytest`.
 
 Some FSL projects (e.g. [`fsl/eddy`(https://git.fmrib.ox.ac.uk/fsl/eddy) use
 CUDA for GPU acceleration. In order to compile these projects, the `nvcc`
-compiler must be available on your `$PATH`, and you must provide the following
-variables:
-
- - `CUDA_VER`: CUDA version, in `major.minor` format, e.g. `10.2`. If not set,
-   defaults to the version reported by `nvcc --version`.
- - `CUDA_HOME`: Path to the CUDA installation that the project should be
-   compiled against. If not set, defaults to `/usr/local/cuda-X.Y`, where
-   `X.Y` is the value of `CUDA_VER`.
-
+compiler must be available on your `$PATH`, or a variable called `$NVCC` must
+refer to the `nvcc` executable to use.
 
 The following additional options may be used to control compilation of a CUDA
 project:
 
- - `NVCC`:        Path to a specific `nvcc` executable
  - `CUDA_STATIC`:  Statically link against the CUDA runtime and certain;
                   CUDA Toolkit libraris (default is to use dynamic linking).
  - `GENCODEFLAGS`: `-gencode` options specifying the device architectures to
@@ -45,8 +37,7 @@ project:
 For example, to compile a CUDA project with a specific CUDA installation, and
 using static linking:
 
-    export CUDA_HOME=/usr/local/cuda-10.1
-    export PATH=$CUDA_HOME/bin:$PATH
+    export PATH=/usr/local/cuda-10.2/bin:$PATH
     make CUDA_STATIC=1
 
 The `Makefile` for each FSL CUDA project may provide additional options for