Update gpu.md

Author: logankilpatrick

docs/src/gpu.md

@@ -49,7 +49,7 @@ m = fmap(cu, m)
 d(cu(rand(10)))
 ```
 
-As a convenience, Flux provides the `gpu` function to convert models and data to the GPU if one is available. By default, it'll do nothing, but loading `CUDA` will cause it to move data to the GPU instead.
+As a convenience, Flux provides the `gpu` function to convert models and data to the GPU if one is available. By default, it'll do nothing, meaning that you can safely call `gpu` on some data or model (as shown below), and the code will not error, regardless of whether the GPU is available or not. If the GPU loads successfully, `CUDA` will cause the data to move to the GPU from the CPU. As is shown below, this will change the type of something like a regualar array to a `CuArray`.
 
 ```julia
 julia> using Flux, CUDA