Document what different `cccl` wheels and conda packages do

This has come up repeatedly internally. Let's add a doc page so that we can cross-reference to it.

- On PyPI:
- `nvidia-cuda-cccl{-cuXX}` is a wheel containing CCCL headers repackaged as part of the CTK release
- the `-cuXX` suffix is dropped starting CUDA 13
- `cuda-cccl` is the CCCL Python wheel
- it works with both CUDA 12 and 13 today
- it includes a private copy of CCCL headers that are not meant to be used by any project
- On conda-forge
- `cuda-cccl` is CCCL headers repackaged as part of the CTK release
- `cccl` is CCCL headers released on upstream (from this GitHub repo)
- `cccl-python` is the CCCL Python package
- it works with both CUDA 12 and 13 today
- it includes a private copy of CCCL headers that are not meant to be used by any project