better doc python interface differences vs cpp, or create more examples

A few cases:

Arg order in relay funcs isn't same as C++, tell folks to prefer named args in python

relay.io.load(node=n,path=p)

leave array vs leaf node acces:

n.fetch("child") vs n["child"] when child is a leaf

Start by reviewing the Python interface documentation and examples around relay.io.load, n.fetch("child"), and n["child"], comparing them with the C++ API behavior. Document the argument-order difference and recommend named arguments in Python, then clarify leaf-node access with examples. Done means these differences and examples are covered clearly.

Written by the indexing model from the issue text.