Mention the obj property which can be assigned additional properties

[silverbucket]

Fixes #335

[silverbucket]

@kernc can we merge this?

[kernc]

@silverbucket Apologies for the long turnaround. I follow the saying, when in doubt, defer. 😅 I understand you found this workaround when you weren't able to assign new attributes to pdoc documentation objects directly due to our use of __slots__?

pdoc/pdoc/__init__.py

Line 520 in 65342ae

__slots__ = ('module', 'name', 'obj', 'docstring', 'inherits')

In that case, with Python becoming leaner in the recent years, I'm questioning the (ancient) use of __slots__ and would probably prefer to simply remove the line ...