[DOC] NUMBA_CUDA_DEBUGINFO is not listed

[dlee992]

NUMBA_CUDA_DEBUGINFO is not listed in this page: https://numba.readthedocs.io/en/stable/reference/envvars.html.
And perhaps this should be renamed to NUMBA_CUDA_DEBUG, since it can be used to set debug option in cuda.jit. This way looks more consistent.

[gmarkall]

There is an Environment Variables section in the documentation that's been brought across to this repo: https://nvidia.github.io/numba-cuda/reference/envvars.html - we can add it there.

[gmarkall]

And, perhaps you're right about DEBUG vs DEBUGINFO, for consistency. Seeing as this was never documented, I think it can be changed 🙂