[issue14979] pdb doc: Explain how to extend debugger instead of sending readers to the source

[Irit Katriel]

Change by Irit Katriel <iritkatriel at yahoo.com>:


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type:  -> enhancement
versions: +Python 3.10, Python 3.8, Python 3.9 -Python 2.7, Python 3.2, Python 3.3, Python 3.4, Python 3.5

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue14979>
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