S3 references in the docstring for Pf8

[jonbrenas]

The docstring for the class Pf8 in pf8.py has not been updated and still says that S3 is the default path (though it is no longer true in fact). @nw20, could you correct that?

[Tanisha127]

Hey @jonbrenas
I came across this issue and would love to help if @nw20 needs a hand.

Here is how I am planning to approach it :
Locate the Pf8 class docstring in pf8.py
Check the current default path being used in the actual code
Update the docstring to reflect the correct default path instead of the outdated S3 reference
Do a quick scan of any related docstrings nearby to make sure nothing else is outdated

It is important fix to keep the docs accurate for users. Happy to submit a PR if you'd like just let me know.