Documentation update for input/output examples

[grinchdubs]

It would be nice to have some examples of what can be used for certain inputs/outputs. For example, Im using the atmosphereField for reflectance however I know its not meant to be used like this but it still works. I just found this out by experimentation

[t3kt]

There's sort of 2 layers to this:

1. What can be connected
2. What is useful in various scenarios

In terms of what can be connected, it's pretty broad. For example, for the translate input on the translate operator, you can use anything that produces a vector (and can be used in the main SDF context). That even includes things like colorRampField, or compositeFields.

For that kind of thing, the best option is to try connecting it and see if you get an error like "Return type not supported: SDF".

So it seems like this is more about what is useful when trying to accomplish various goals. For that, I think the only really solution would be an exhaustive collection of snippets/examples like TD's "OP Snippets".

Those efforts are tracked under #132.