Fixed typo on cmake command. Added note about building for Apple Silicon

[deanwampler]

The cmake command needs ../.., not ...

I added a note about the cmake command for Apple Silicon.

[Syllo]

Not sure if I follow:

# This clones into the nvtop directory (by git's default cloning in a directory with the repo's name)
git clone https://github.com/Syllo/nvtop.git
# Create a build directory in nvtop and switch to it
mkdir -p nvtop/build && cd nvtop/build

So at that point, the directory should look something like:

ntop
├── CMakeLists.txt
└── build <- we are here

Hence, I don't see the point of the second parent directory to the cmake command since CMakeList.txt is in the direct parent.

I could perhaps update the documentation with more recent cmake commands like cmake -B nvtop/build -S nvtop && cmake --build nvtop/build