Add examples for types of custom nodes

[robinjhuang]

https://www.comfydocs.org/essentials/custom_node_overview

Would be great to add an example for each of the types:

1. Server side only
2. Client side only
3. Independent Server Client Side
4. Connected Client Server Side

[chrisgoringe]

I can put that into the workplan :)

[robinjhuang]

Thank you @chrisgoringe !!

[chrisgoringe]

Clarification question... did you mean (a) or (b):

(a) Point to an example of each type of node, either in the core package, or an existing custom node, and explain briefly why it is in this category

(b) Provide a code-complete example of a (simple) node in each category

Either is fine, obviously (b) is a bigger task!