Change docs about kwargs

Summary:
I removed the statement that kwargs do not exist in the ATen dialect.
Look at T160625628 for more context.

Reviewed By: kimishpatel, larryliu0820

Differential Revision: D48484077

fbshipit-source-id: 997bb76f085404fcf94995599e76d97ccb29bbd4

Author: angelayi

docs/website/docs/ir_spec/00_exir.md

@@ -213,9 +213,10 @@ A `call_function` node represents a call to an operator.
 1. In FX graph, a call_function can refer to any callable, in EXIR, we restrict
 this to only Canonical ATen operators (a select subset of PyTorch ATen operator
 library), custom operators and control flow operators.
-2. In FX graph, calling with both args and kwargs is allowed, in EXIR, only args
-will be used, kwargs will be an empty dict.
-3. In EXIR, constant arguments will be embedded within the graph.
+2. In EXIR, constant arguments will be embedded within the graph.
+3. In FX graph, a get_attr node can represent reading any attribute stored in
+the graph module. However, in EXIR this will only be reading submodules as all
+parameters/buffers will be passed in as inputs to the graph module.
 
 
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