gh-91555: add warning to docs about possibility of deadlock/infinite recursion (GH-135954)

* gh-91555: add warning to docs about possibility of deadlock/infinite recursion

Attempt to clarify in the documentation that care must be taken when using
multiprocessing classes to implement logging since they have builtin internal
logging, and hence may cause deadlock/infinite recursion.

* Update Doc/library/logging.handlers.rst

Co-authored-by: Vinay Sajip <vinay_sajip@yahoo.co.uk>

* Change whitespace.

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Co-authored-by: Vinay Sajip <vinay_sajip@yahoo.co.uk>