Doc Issue : Fork can build lenses to set values on multiple lenses

[yellowbean]

https://python-lenses.readthedocs.io/en/latest/tutorial/optics.html#setters

This method allows you to create a setter that can set at two different places at once.This method allows you to create a setter that can set at two different places at once.

Actually the Fork allows user to set a setter can set more than two different places at one

lens.Fork(lens[0], lens[-1],lens[2]).set(10)([1,2,3,4,5,6])