DOC: Debugging flag usage is not described well

[cluhmann]

Issue with current documentation:

The debugging FAQ states that:

Using the PyTensor flag optimizer=fast_compile or optimizer=None can often tell you the faulty line, while exception_verbosity=high will display a debug print of the apply node.

But nowhere in the FAQ is there any information about how to actually use such flags.

In addition, the "code" specified in these examples appears to be incorrect in that None and high must actually be strings (more obvious that high must be a string, but None looks like python's None rather than the string "None").

Idea or request for content:

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