cuda_core: add "10 minutes to cuda.core" tutorial to docs

Add a beginner-friendly "10 minutes to cuda.core" guide that walks through
the core workflow (select a device, compile a kernel, allocate memory, copy,
launch, time with events, use multiple streams, capture a CUDA graph, and
interoperate with CuPy/PyTorch), then wire it into the cuda.core docs table of
contents between the installation and examples sections.

Signed-off-by: Sri Koundinyan <skoundinyan@nvidia.com>

Author: sri-koundinyan