Adds a note explaining that default CMake versions on systems like
Ubuntu 22.04 LTS might not support newer CUDA dialects (e.g., CUDA 20),
leading to specific build errors.
Recommends installing a newer CMake via the Kitware APT repository
as a resolution. This helps users troubleshoot errors like:
"Target ... requires the language dialect 'CUDA20', but CMake does not know the compile flags..."
* Consolidate the installation section, as it's currently too cluttered
* Move the Multi-GPU section to the top-level structure
* Add a **detailed** tutorial on registering extra GPU memory with Marlin