Add more documentation for model local function

[jcwchen]

Feature Request

System information

ONNX version (you are using): 1.11

What is the problem that this feature solves?

ONNX has introduced model local function for a while and brought a few enhancements about it recently. Going forward it will be more and more useful and popular so ONNX should add more documentation about it for user reference.

Describe the feature

We can add a new standalone document for it or at least describe it more in the IR.md.

Will this influence the current api?

No.

Feature Area

Model location function, documentation.

[gramalingam]

Created PR #4180