Propose documentation addition for INPUT_TYPES

[corbin-hayden13]

I propose an addition to custom widgets documentation regarding passing serialized custom widget data from javascript to python. Credit goes to rgthree for finding an awesome solution:

This ContainsAnyDict class creates an easy way to receive serialized data from custom widgets from javascript as kwargs to the FUNCTION in python whereas even if the custom widgets were serialized they would not be passed to the function in any capacity.

class ContainsAnyDict(dict):
    def __contains__(self, key):
        return True
...

@classmethod
def INPUT_TYPES(s):
    return {
        "required": {},
        "optional": ContainsAnyDict()
    }

[chrisgoringe]

Thanks. I'm not making changes here any more, instead I'm working on the documentation at docs.comfy.org. I'll be adding this over there!