Add documentation for RAPIDS_NO_INITIALIZE

[charlesbluca]

Adds a warning to the UCX docs explaining the hazards of starting a CUDA context before initializing a UCX cluster, and how RAPIDS_NO_INITIALIZE can sometimes be used to avoid this.

[codecov-commenter]

Codecov Report

Merging #898 (e10d4b8) into branch-22.06 (7a0c2c2) will not change coverage.
The diff coverage is 100.00%.

❗ Current head e10d4b8 differs from pull request most recent head 97f4fbe. Consider uploading reports for the commit 97f4fbe to get more accurate results

@@              Coverage Diff              @@
##           branch-22.06     #898   +/-   ##
=============================================
  Coverage         89.49%   89.49%           
=============================================
  Files                16       16           
  Lines              2094     2094           
=============================================
  Hits               1874     1874           
  Misses              220      220           

Impacted Files	Coverage Δ
dask_cuda/explicit_comms/comms.py	98.87% <ø> (ø)
dask_cuda/local_cuda_cluster.py	88.17% <ø> (ø)
dask_cuda/cuda_worker.py	76.54% <100.00%> (ø)

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[pentschev]

Overall looks good, but I requested a few changes to make it more accurate and descriptive. Thanks @charlesbluca .

[charlesbluca]

Thanks @pentschev 🙂 think this should be ready for re-review / approval

[pentschev]

LGTM, thanks @charlesbluca !

[pentschev]

@gpucibot merge