Accuracy section in User Guide

[philipc2]

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          > > Also some introduction for our constants will be helpful as well

constants intro is more of a subject for the developers guide

There are still some useful constants for the users.

For example, when the users are using our package, knowing what's the smallest value for the relative error tolerance is also important.

Originally posted by @hongyuchen1030 in https://github.com/UXARRAY/uxarray/issues/472#issuecomment-2099273456